In the paper, Step sinus pulse width modulation (SSPWM) three phase inverter is tested on a nonlinear device which can produce harmonics. There are 12 switches on active and passive cases. On the inverter, operations of switches are provided by arranged SSPWM which can be calculated with similarity rules of triangles. A mathematical model of inverter is obtained with operating characteristics of the switches determined. SSPWM technique is used to control non-linear devices as thyristor and rectifiers which are widely used in electronic systems. So, single phase alternating voltage is converted to direct voltage with rectifier circuit to provide input voltage of inverter. After that, Six switches of common three phase inverter model are connected to six thyristors controlling inputs and outputs of three phase loads so that performance of SSPWM can be investigated on high level harmonic of loads. The inverter load of resistive (R) and inductive (L) are performed at the MATLAB Simulink so that SSPWM technique could be showed the reducing effect of the harmonic on loads. So, SSPWM and SPWM controlling inverter are performed on frequencies. Then, performances of common SPWM and SSPWM running nonlinear loads are compared with results.