Abstract: In operation process,key of stable operation of permanent magnet linear synchronous motor is wether it is out-of-step.Through analysis of characteristics of power angle of permanent magnet linear synchronous motor,the paper put forward a prevented control strategy of out-of-step of motor combining changing voltage with changing ratio of voltage and frequency,which uses double-mode fuzzy controller to achieve prevented control of out-of-step of motor.The simulation result showed that the strategy has simple arithmetic,good quality control,and so on,which can avoid out-of-step operation of permanent magnet linear synchronous motor effectively,and has higher application value.