Abstract： To meet the demand of the non-overload characteristic of medium specific speed multistage centrifugal pumps, a formula for the design of impeller was derived by using empirical correlations, based on the theory of non-overload. Two pumps, the specific speeds of which were 89.3 and 135.0, were designed using this formula and the traditional formula, and the performance curves were obtained using Fluent. The results indicate that the extreme point of shaft power curve appeares in both of the pumps designed using the derived formula, and the coefficient K, the ratio of the maximal axle power to the power in designed working condition are 1.13 and 1.03, validiting the derived formula. Compared with the pumps designed using the traditional formula, the head of the pumps designed using the derived formula increases by 14.0% and 7.5%, and the efficiency increases by 2.68% and 1.03%. Meanwhile the radial dimension becomes smaller. The derived formulas can be used for medium specific speed non-overload multistage centrifugal pumps.