Abstract: Two compressors with wedge-shaped diffusers were designed.One of them has back-swept impeller and the other with ordinary impeller.Numerical simulation was conducted on the two compressors to find out the difference between their performance.The effect of being back-swept in performance and secondary flow was analyzed.The difference in performance between the compressor with 19 diffuser blades and the other with 23 diffuser blades were studied.The results showed that back-sweptness reduced the flow range of the compressor.Near the impeller inlet,there existed differences between the secondary vortexes.