Efficiency of low specific speed centrifugal pump is low and difficult to improve due to larger diameter, smaller outlet width of the impeller and serious channel diffusion. However, gap drainage technology has significantly improved pump performance. In order to analysis the effects of gap drainage blades on different low specific speed centrifugal pumps performance, the conventional and gap drainage impellers of different specific speed were designed, and the same specific speed impellers were tested in the same volutes, respectively. The experimental results show that gap drainage technology effectively improved the performance of distortion blade impellers. The degree and region of impact on low specific speed centrifugal pumps performance varies with specific speed. The smaller wrap angel and gap, the more favorable to improve performance.