The inner cavity of three-way valves is mostly polished by hand， which holds low processing efficiency， high labor intensity and poor environmental friendliness. In this regard， this paper carries out simulation analysis and experimental verification of the flow field of abrasive flow finishing in the inner cavity of a three-way valve. By establishing a flow field simulation model and comparing the flow field distribution with and without core molds， a special profiling fixture is developed and experimentally verified. The experimental results show that the roughness value of the inner wall surface of the valve is significantly reduced when the mandrel is used， with the reduction rate of the big end of 77.79% and the small end of 77.26%， which far exceeds the reduction rate of the coreless processing （15.05% for the big end and 11.62% for the small end）. Therefore， using the mandrel can significantly improve the processing quality， as well as the processing efficiency.