Abstract:The unstable boundary of compressor include stall boundary and surge boundary which have an important influence on the compressor’s characteristics，even cause serious damage to it， so making clear the internal flow field near stall pointhas important significance. This paper took a 2. 5 stage transonic axial flow compressor as research object，the compressor’s characteristic curves include all operating conditions at seven speeds were calculated by CFX. This paper focuses on the internal flow field near stall point， contrasts near the design point and near plug flow， explores the stall characteristics and mechanism of multistage axial compressor. Adjust the angle of the inlet guide vane，rotate the vane toward the suction surface of the front edge and the opposite direction by the same angle，calculate the characteristic line at 50%，80% and 100% design speed. It is not difficult to find out under the middle and high speed，the flow pressure characteristic line moves downward to the left， the efficiency pressure characteristic line moves more obviously. It comes to conclusion，the inlet guide vane rotates toward the suction of the front edge of the blade direction can delay stall.