This paper proposes a novel technique to reduce the detent force in permanent magnet linear synchronous motor (PMLSM) using auxiliary poles. The detent force that is caused by the attraction between permanent magnet (PM) and the iron core without input current can be divided into two components: the slot effect and the end effect. To reduce these two effects, we analyze the characteristics of the detent force according to semi-closed slot clearance length and auxiliary poles position by using two-dimensional (2-D) finite element method (FEM). The numerical calculations and the experimental results prove that this proposed technique has a good effect on the reduction of the detent force.