This paper is the result of pump performance test that has the aim to suggest an another way of the pump design based on the energy saving. In the pump used in building facility, the shaft power is calculated by the total head and capacity applying the listing pump efficiency according the shape of pump. Also the motor output is calculated by applying the margin of loss according to the connecting state of the shaft and the motor. Then it is the general way to choose the higher standard model than the above calculated motor output in deciding the size of pump lastly. In result the motor output is often determined in too large size by adding the additional margin. Therefore it is necessary to certificate whether this way is the most effective method in the aspect of the energy consumption and the efficiency. This research suggests the another advanced way. It is to choose the motor output size with no considering the additional margin than the higher model that the additional margin is added unconditionally from the calculated motor output. This paper is the research for the relative relationship of the power margin rate and the efficiency in design of pump model. In the result of the pump performance test by two model pumps choosen in the general way, and suggested way which is higher about 17% in the aspect of the efficiency and higher about 18% in the energy saving comparing with the general method. Finally this research shows that the suggested method is an applicabal way to save energy by using the most appropriate pump.