Step sinus pulse width modulation (SSPWM) multilevel inverter is designed in order to control loads with reducing nonlinear effects as harmonics. Multilevel inverter has six switches for every phase and the switches are connected to control inputs and outputs of load. This method focuses on the identification of twelve IGBT and six MOSFET switches as nonlinear device, which consists of only the active and passive switches in three phase multilevel inverter. Inverter switches operate with pulse width modulation after signals of six step sinus compare with 2-small triangle signals for every phase. While operating characteristics of the switches are determined, a mathematical model of inverter controlling loads can be formed. After that, two PWM techniques are used to investigate the non-linear effects on this circuit model which contains mixed switches in its structure. So, the inverter load of ohmic (R) and inductive (L) are performed at the simulation so that performance of SSPWM multilevel inverter could be showed on loads. So, SSPWM and SPWM controlling inverter is tested on frequencies and modulation indexes. Then, performances of SPWM inverter and SSPWM multilevel inverter running loads are compared with output results.