In order to analyze the issue of flow characteristics of 3-way proportional valve in pipeline system，the paper carried out the numerical simulation of three-dimensional flow field to the actual size of 3-way proportional valves, and analyzed the variation law of the proportion of outlet flow and head loss ratio with the change of inlet Re and position of valve core. While the 3-way valve is used to mix flow ,it analyzed the variation law of inlet flow with pressure difference of outlet and in let.The conclusion are that the flow rate of proportion valve is mainly affected by valve core position and the better way to reduce the local resistance is to reduce Re of the inlet in the condition of certain mid-stream forms and wall roughness. The method realized optimization control based on characteristics curve of flow proportion.