The aim of this paper was to find an appropriate water film thickness to improve the volumetric efficiency of water hydraulic motor and the static and dynamic characteristics of the supporting shaft rotor pair. Based on the equilibrium equation and the flow equation, the mathematical models of the power loss, the static characteristics and the dynamic characteristics were established. The total power loss, the bearing capacity, the static stiffness, the radial velocity and the displacement of rotor could be the performance indexes of the supporting shaft rotor pair. Different size of the water film thickness had different performance indexes. So the influence of the water film thickness on the supporting shaft rotor pair was analyzed in detail. The research showed that when the water film thickness was increased, the power loss, the radial velocity and the displacement of rotor were increased, the static stiffness and the volumetric efficiency were reduced, but the bearing capacity kept constant. 