The output voltage characteristic of photovoltaic cell is soft, so the DC-DC switching converter in the system needs a wide range of working voltage, and the reasonable design of converter parameters is the prerequisite for its safe and reliable operation. Taking the Buck-Boost converter widely used in stand-alone photovoltaic power generation system as an example, the working principle of the converter is analyzed, and the influence of inductance and capacitance on the working mode and output ripple voltage of the converter is discussed. On this basis, the design method of inductance and capacitance parameters for wide input and wide output voltage range is given. Through simulation analysis, the rationality of parameter design of Buck-Boost converter with wide voltage range is verified.