From Fig. 5, it can be known that the change regular of head keeps constant at first and then descends with the decrease of NPSH. The head of model pump grows with the increase of blade number of impeller. When the blade number is 7; the head of model pump obtains the maximum value. The NPSHR of model pump with blade number from 4 to 7 are 3.87 m, 3.58 m, 4.30 m, and 4.82 m, respectively, which are obtained by using interpolation method basing on Fig. 5.