The survey shows that the annual discharge of urban sewage in China can reach about 40 billion tons. With the acceleration of urbanization, the discharge of sewage will continue to increase. According to the experts, about 40% of the low-level waste heat in the city is in the potential urban sewage. The reasonable recovery of this part of low-level heat and the simultaneous recovery and utilization of the water and heat of urban sewage treatment not only realize the recovery and utilization of urban waste heat, turn waste into treasure, but also develop a new renewable and clean energy utilization mode, which opens up a new way for the recycling of urban sewage and low-grade clean energy, which can be said to achieve two goals with one stone.The research shows that urban sewage has the characteristics of large water volume, suitable and stable temperature, small seasonal variation, warm winter and cool summer, so it can be used as a good low-level renewable energy. The primary sewage source heat pump uses urban sewage as a cold and heat source. According to the characteristics of sewage temperature higher than outdoor temperature in winter and lower than outdoor temperature in summer, the heat energy that is difficult to be directly used in sewage is extracted by heat exchanger, sent to the intermediary, and then transmitted to the heat pump host to form high-temperature water for heating in winter. This system can also be used in reverse for cooling in summer.Winter heating in northern China depends on coal, oil and natural gas. Heating and environmental protection have become a pair of difficult contradictions. Urban sewage is a rare heat pump cold and heat source in the cold regions of the north. Its temperature is relatively stable all the year round. It is higher than the ambient air temperature in winter and lower than the ambient air temperature in summer. This temperature characteristic makes the sewage source heat pump operate more efficiently than the traditional air conditioning system, and the effect of energy saving and operation cost saving is remarkable. As one of the application forms of the ground source heat pump technology, the promotion of the original sewage heat pump technology is an effective way to change the current situation of the energy consumption structure in cities, which is mainly coal-fired, and it also opens up a new space for the application and development of renewable energy.Experts introduced the operation mode of the sewage source heat pump air conditioning system, so that the ratio of energy input to output can reach 1:4, that is, the input of 1 kilowatt of electric energy can reach more than 4 kilowatts of heat, saving 30% - 75%. The heating fee is 70% compared with coal-fired heating, 50% compared with gas and 30% compared with oil. When heating, each ton of sewage can obtain 5000-10000 kW of heat energy, which is equivalent to the effective heating value of 1.5kg-3kg standard coal.The sewage source heat pump system is a cold and heat source for heating in winter, air conditioning in summer and domestic hot water supply throughout the year. The boiler room systems such as coal, gas and oil are omitted for heating, and there is no combustion process, which avoids smoke exhaust pollution. The cooling tower is omitted for cooling, which avoids noise, mold pollution and air pollution of the cooling tower. Do not discharge any waste residue and wastewater into the atmosphere; The exhaust gas and soot have truly realized zero pollution and remarkable environmental benefits.Under the current situation of global energy crisis and serious environmental pollution, the energy potential contained in urban sewage is huge and it is a clean energy that will not produce pollution. Therefore, the recovery and utilization of low-level energy in urban sewage not only helps to deepen people's comprehensive understanding of the recycling of urban sewage, realize the recycling of resources, turn waste into treasure, and fully reflect the concept of "developing circular economy"; Thus, it can greatly improve the energy utilization rate of the city, reduce the dependence of the city on fossil fuels, and have great practical significance for controlling air pollution, protecting the global environment and building an energy-saving city.The successful implementation of many projects has proved that the use of primary sewage source heat pump system for heating and cooling has achieved an energy saving rate of 30% ~ 75%, which truly realizes zero emission and zero pollution, and does not discharge any waste gas, waste and waste residue into the atmosphere. Its investment and operation costs are also much lower than those of traditional methods. The vigorous development can save hundreds of millions of tons of coal per year, which will also reduce a large amount of greenhouse gas emissions.Nowadays, the construction of green ecological civilization has become the focus of common concern of all walks of life. The sewage source heat pump system integrates many highlights such as energy conservation and emission reduction, low-carbon environmental protection, renewable and clean energy utilization, and lays a good foundation for the smooth progress of energy conservation and environmental protection in China.