Abstract: An improved quasi-Z-source inverter is proposed,which can improve the boost capability of the inverter and reduce the harmonic content of the output voltage by integrating the improved“multiplier voltage cell”. Improper parameter design of high-order nonlinear system will lead to sub harmonic oscillation and chaos. In order to solve the problem about system parameter design and instability caused by the nonlinear behavior of switching power supply,the dynamic model of the inverter with second harmonic ripple in CCM mode is constructed. Then the nonlinear behavior of PI controlled inverter is studied. The influence of different input parameters and second harmonic ripple on the system stability is analyzed,which could provide a reference for the parameter optimization and stability design of the inverter. Finally,a 1000 W prototype is built to verify the correctness of the theoretical analysis.