The best efficiency point prediction of the pump as turbine (PAT) is one of the key issues for its application. In the present paper, a theoretical method based on the impeller-volute matching principle was proposed to predict the best efficiency point of PAT and validated by three centrifugal pumps with specific speeds from 58.7 to 129.6 with an error of less than 5%. In the next step, a single-stage centrifugal pump with specific speed of 90 under normal rotation speed was investigated by experiment and the best efficiency point for pump and turbine modes were obtained. The experimental results of the head and discharge conversion factors and the predicted results obtained through theoretical or statistical methods were compared to verify further the effectiveness of the method proposed in this paper. The performance curves of the pump and turbine modes were predicted using numerical methods and verified by experiment. The hydraulic loss of the main components was calculated to obtain a deeper understanding of the variations of best efficiency point of PAT under different rotation speeds. Finally, the best efficiency point of PAT under different rotation speeds predicted by the theoretical and statistical methods was compared with the numerical results. (c) 2020 Elsevier Ltd. All rights reserved.