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A reversed running centrifugal pump can work as a hydraulic turbine. In order to improve the operating performance of pump as turbine (PAT), a special impeller with forward curved blades was designed and experimented. By using the constant velocity moment theory, the calculation expressions of volute constant within spiral volute were developed and the velocity moment before impeller was acquired. Impeller with forward curved blades was designed and manufactured. Its inlet angle at leading edge was determined by using shockless inlet flow while its outlet angle was designed on whirl free outlet flow. Performance test of PAT with designed forward curved blades impeller and conventional back swept blades impeller was performed. The comparison between designed forward curved blades and conventional back curved blades shows that the best efficiency is increased by 13.22%. Compared with original PAT performance curves, the efficiency curve of PAT with forward swept blades is more flat. The efficiecy variation of PAT with forward curved blades is only within 1.5% between 0.9QBEP (flow rate of best efficiency point)and 1.2QBEP operating range. Therefore, the high efficiency operating range of impeller with forward swept blades is wider than conventional back swept impeller.