Abstract: The PM linear motors（PMLMs） with fractional slots per pole can adopt non-overlapping windings,so they have many advantages such as short end windings,low copper losses,high thrust force density and so on.They are widely applied in high speed digital machine tools and processing equipments of semiconductor.For two PMLMs of 12 slots/11 poles and 12 slots/10 poles,four feasible structures of each one are described with types of single-sided or double-sided and windings of all teeth wound or of alternate teeth wound.Based on the erected finite element method（FEM） model,the relationships between the average thrust force,thrust ripple and structure parameters are investigated.Moreover,the thrust force performance of the double-sided structure is deeply studied when permanent magnets in two sides are shifted by a certain position,and then the optimal shifted position is found.By comparative analysis in detail,the optimal designs of single-sided and double-sided PMLMs with fractional slots per pole are obtained based on the lowest thrust ripple/thrust force.The research results are benefit to optimal design and application of these kind PMLMs.