Abstract: Longitudinal end effects of permanent magnet linear synchronous motor（PMLSM） have been no accurate and easy methods to analyze due to the over-complex flux distribution at the ends.Therefore,it is difficult to evaluate the performance of various measures for reducing longitudinal end effects.In this paper,the flux distributions have been calculated on the basis of the magnetic circuit analytic model.Then a new conclusion has been attained by comparing the difference of flux distributions between PMLSM and permanent magnet rotating synchronous motor（PMRSM）.Longitudinal end effect is essentially a magnetic boundary which distorts the flux distribution of the motor.Some easy and convenient methods to reduce the longitudinal end effects have also been achieved by this conclusion.Then the methods are used to reduce the detent forces of the fractional-slot motor and integral-slot motor.Finally the detent force is decreased by 80% with the methods.They have been proved to be correct in finite element simulation and experiment.