Proportional flow valve is one of key parts in automatic transmission, and its performance directly affects quality and effect of transmission system. The proportional flow valve of automatic transmission was studied,the key parameters’ effect on performance was analyzed by simulation. Through structural analysis, the valve was divided into electromagnetic part and hydraulic part. The key parameters of electromagnetic part,such as air gap and armature size of the electromagnetic part, were analyzed with Ansoft Maxwell; the p-i characteristics, following characteristics and dynamic response characteristics of the hydraulic part were analyzed with AMESim software. Forward design and optimization design were performed by simulation calculation. Experimental results verify the design’s rationality and simulation’s reliability.