Different from the reaction turbines, the hydraulic performance of Pelton turbine is dynamic due to the unsteady flow in the rotating buckets in time and space. The dynamic energy efficiency of bucket ηEB and power efficiency of bucket ηPB within a short period can be predicted from the dynamic flow pattern of the free-surface sheet flow in the rotating bucket, whereas the dynamic discharge efficiency of bucket ηQB is defined as the resident discharge in the bucket at the respective moment. Under the operation of higher unit speed nDH than the optimum one, the power efficiency of bucket is deteriorated by the jet interference with the rear surface of bucket ?Prear at the first stage of the dynamic performance, as well as the loss power due to the spilt flow from the cutout of bucket at the later stage of performance. Based on the dynamic performance prediction presented, the future possibility of the quantitative investigation for the negative scale effect of Pelton turbines was discussed. Different from the reaction turbines, the hydraulic performance of Pelton turbine is dynamic due to the unsteady flow in the rotating buckets in time and space. The dynamic energy efficiency of bucket ηEB and power efficiency of bucket ηPB within a short period can be predicted from the dynamic flow pattern of the free-surface sheet flow in the rotating bucket, and the dynamic discharge efficiency of bucket ηQB is defined as the resident discharge in the bucket at the respective moment. Under the operation of higher unit speed nDH than the optimum one, the power efficiency of bucket is deteriorated by the jet interference with the rear surface of bucket? Prear at the first stage of the dynamic performance, as well as the loss power due to the spilled flow from the cutout of bucket at the later stage of performance Based on the dynamic performance prediction presented, the future possibility of the quantitative investigation for the negative scale effect of Pelton turbines was dis cussed