The load distribution of the impeller and the shape of blade bone surface as well as the pump performance are determined by the circulation distribution from the impeller inlet to the outlet. However, perfect conclusions about optimal forms of the circulation distribution have not been seen yet. In this paper, three kinds of circulation distributions were studied. Three mixed flow pump impellers with high specific speed were designed according to the circulation distributions, and the models of the three pumps were built and modeled in the commercial CFD code ANSYS-CFX 11.0. The flow field in the pumps has been investigated using large eddy simulation (LES). Experiment was carried out on one model. And the performance curves predicted by LES were compared with the experimental data, and good agreements were achieved. The results show that: there is a low pressure area at impeller outlet. The pressure distribution along the circumferential direction was asymmetry at the front-end area of guide vanes, but it becomes uniform at the end of guide vane. The bearing pressure on the pressure side of the model 2 is lower, and the pressure distribution of model 1 is more asymmetry and there is a clear low pressure area at outlet of blade; Cavitation performance of model 2 is better, and the maximum efficiency is also the highest, but the hump is more serious; Model 1 has a widest area of high effective area.