In order to improve the efficiency of the hollow ultrasonic motor， the effective electromechanical coupling coefficient of the motor stator is analyzed. Firstly， the piezoelectric impedance characteristics of the motor stator are analyzed by using the equivalent circuit method， and the calculation method of the effective electromechanical coupling coefficient is determined. Then the finite element simulation of the piezoelectric impedance characteristics of the motor stator is carried out by ANSYS software， and the influence of the vibration mode of the stator， the structure size of metal elastomer and piezoelectric ceramic on the effective electromechanical coupling coefficient is analyzed. According to the simulation results， four different stators are designed and manufactured， and the four stators are tested by impedance analyzer. The relative errors between the measured values and the simulation values are less than 10%. The impedance characteristic curves obtained are consistent with the simulation results. Finally， the four stators are assembled into the prototype， and the motor performance test platform is built for experimental test. The results show that the four prototypes have achieved good output performance. Combined with the experiment， it is proved that increasing the effective electromechanical coupling coefficient of stator can obtain lower power consumption and improve the output efficiency of motor， which has high engineering application value.