At present, there are several application examples of distributed energy system in China, which can provide flexible supply of energy, but have some shortcomings such as low operation efficiency, poor economic performance and so on. In order to improve the primary energy ratio of distributed energy system, a demonstration project of efficient combined cooling and power system using natural gas has been built, which relied on three buildings located at the Foshan Power Supply Bureau. According to the problems of low primary energy ratio and backpressure of gas turbine exhaust over the limit in demonstration project, the transformations were carried out for the main engine and coherent system. The results show that the annual primary energy ratio of distributed energy system depends on four aspects of factors: the efficiency of main equipment, the waste heat utilization of flue gas, the equipment load and the operation time per year.