Abstract: Detent force,as one of the principal elements of thrust ripple,is also a primary factor to evaluate the performance of permanent magnet linear synchronous motor （PMLSM）. On the basis of the magnetic circuit analytic model,detent force has been calculated by energy law theory and the key factors influencing thrust ripple have also been analyzed. Consequently effective measures to diminish the detent force have been achieved either by setting an appropriate shape of slots or by changing the shapes of the outlet edges. It has been testified by finite element simulation and relevant experiments to be correct in theoretical calculation and conclusion.