As the existing researches on the water cooling system of motors applied to electric vehicles mainly focus on the heat exchange performance without taking full consideration into pressure loss,the influences of cooling channel parameters on heat exchange performance and pressure loss are analyzed theoretically for the frequently- used driving motor-permanent magnetic synchronous motor ( PMSM),finding that the twist number of cooling chan- nels influences heat exchange and pressure loss greatly,and that the transverse dimensions of cooling channel have little influence on heat transfer but have great influence on pressure loss.Thus,an optimal range of cooling channel parameters is obtained,with its validity being verified by simulating PMSM temperature field and pressure loss of cooling channels with optimized parameters through a finite element analysis.Finally,a new design method of cool- ing channels considering both heat exchange and pressure loss is presented.The research provides a reference for the design of water cooling system of PMSM with high power density.