Voltage mode Buck-Boost converter is a typical non-minimum phase system. According to the working characteristics of the DC-DC buck-boost converter, the small signal model is established by using the state space average method, and the Proportional-Integral(PI) controller parameters are designed. Buck-Boost converter is a time-varying nonlinear system. Traditional PI control is difficult to achieve the optimal control effect, so the fuzzy PI control is adopted to avoid the disadvantages of PI control. Aiming at the problem that the control precision of fuzzy PI control becomes worse when the controlled variable changes greatly, a variable universe fuzzy PI controller with adaptive scaling change in the fuzzy universe is designed to control the Buck-Boost circuit. Through Matlab/Simulink environment simulation, the experimental results show that the variable universe fuzzy PI control has better dynamic control performance.