This　research　aims　at　investigating　the　flow　in　PWS.　A　3D　unsteady　flow　model　of　the　PWS　was　completed　based　on　the　way　of　CFD.　In　order　to　gain　the　boundaries,　parameters　were　tested　by　PWS　test　system.　The　PWS　3D　unsteady　flow　model　is　available　to　simulate　the　flow　both　within　the　rotor　and　casings　at　different　rotational　speeds　with　good　agreement　with　experimental　results.　The　results　give　the　clue　that　the　optimum　high　rotor　rotation　speed　can　help　the　PWS　gain　satisfied　performance.