This paper analyzes the modular design method of the photovoltaic power generation system and presents a 5KW solar power inverter with variety of operating modes. Depending on the signal interface model, the hardware circuit is divided into several modules, including DC-DC main power circuit, DC-DC control circuit, DC-AC main power circuit, DC-AC control circuit and auxiliary power supply module. The circuit detail design is given and this system has been already used in the solar power stations. The circuit has a reusable and beneficial photovoltaic inverter standardized design. The experiment results prove that this system has features of reliability, easy maintenance, strong scalability and meets the requirements of the solar-energy generation system.