This paper proposes a novel three-phase unilateral three-level inverter which uses Pre-Boost converter to implement three-level power supply and adopts three-level on one side and two-level on another side in the inverter part to simplify the circuit structure. It analyzes the working principle and proposes a five segment work mode space vector pulse width modulation(SVPWM) strategy which can implement normal modulation on the three-level side and low loss modulation on the two-level side．Under this strategy, the circuit has a relatively simple control algorithm, and can still achieve lower switching loss and less harmonic content of output voltage and current while reduce the volume of the inverter. Modeling in MATLAB/SIMULINK, the simulation results verify the effectiveness and superiority of the new type circuit and the feasibility of its modulation strategy.