Abstract: In order to improve the reliability of user side power supply and the cleanliness of electrical energy, a system capacity optimization configuration and operation strategy based on the "grid light storage diesel" joint power supply mode is proposed. First, the optimization configuration method of the joint power supply system has been comprehensively analyzed from the aspects of photovoltaic, energy storage, and diesel generators. Then, the "grid-photovoltaic-storage-diesel" joint power supply mode has been formed, which introduces photovoltaic and energy storage into the traditional "grid-diesel generator" power supply mode. And propose the power supply structure and operation strategy of the joint power supply system. Finally, a case study will be used to analyze and verify the reliability of the proposed optimization configuration method and operational strategy. It can be obtained that the "grid-photovoltaic-storage-diesel" combined power supply mode has significant effects on improving the reliability of user power supply while being economical.