Abstract: A new three-stage compressor has been made by scaling up a two-stage transonic compressor and adding a third stage in order to enhance its mass flow and pressure ratio.Its tests show that serious flow mismatch exists between second stage and third stage.Factors for the flow mismatch are found out as effect of scaling up coefficient on flow block factor,variation of its rotor blade airfoil section stagger angles due to centrifugal force and the unsteady effect for supersonic blading with low aspect ratio.Owing to above mentioned three factors,the flow capaility of third stage is increased by 6 3%.Tip-cut of the third stage demonstrates that the flow-path-area of the third stage is reduced to 93 7% and modified three-stage compressor has good flow match between the second stage and third stage, as a result its surge margin is enhanced by 5 8%.