In order to explore the influence of stator gap width on the electromagnetic performance in permanent magnet( PM) machines with different slot-pole configurations and different modular structures, the simulation models of 12s-10p and 12s-l4p inegrated, E-core modular and C-core modular PM machines were carried out by finite element (FE) software. By changing the stator gap width , the relationship between the stator gap width and the electromagnetic performance was obtained and verified by theoretical analysis. The results show that 12s-10p machine is more suitable to adopt C-core 2mm/4mm modular structure to reduce cogging torque and torque ripple, while 12s-14p machine is more suitable to adopt E-core 4mm modular structure to increase output torque or C-type 2mm to reduce cogging torque and torque ripple.