A semi-analytical approach was applied for armature reaction field analysis of surface mounted permanent magnet brushless motors. The field region was divided into air-gap and slot sub-regions. Analytical method was used to solve the air-gap field equation while the difference method to solve the field equation in slot region. Computation results in common parts can be used as boundary conditions for another region. Stator slot opening and slot currents can be presented on fact. The proposed approach is exemplified by using practical permanent magnet brushless machines, and verified by comparing with the finite element method and experiment.