By analyzing the mathematical model of asymmetric single-phase induction motor (SPIM) in different forms, the problems of oval magnetic field and asymmetric operation of SPIM are solved. The rotor flux is calculated by a voltage-current hybrid model rotor flux observer, and the rotor flux position and rotor speed are further calculated. Based on the three-leg inverter, the simulation of speed sensorless vector control of SPIM with rotor-field orientation is carried out, the feasibility and effectiveness of the control system are verified.