Sliding bearing pair is one of the important friction pairs within water hydraulic axial piston pump, which can result in significant influences on the pump’s performance. Generally, owing to the characteristics of low viscosity and poor lubrication of water, the sliding bearing will operate under condition of dry or mixed lubrication, leading to a severe adhesives wear and material softening. In order to investigate the flow field of the sliding bearing in hydrodynamic condition, the effects of the water film pressure distribution, load carrying capacity changing with radial clearance and width–radius ratio of the sliding bearing pair have been simulated through MATLAB. And a suitable material combination of the sliding bearing pair was selected though a custom-manufactured friction and wear test rig. Based on the theoretical and experimental studies, an appropriate structure of the sliding bearing within water hydraulic axial piston pump was designed. The loading experiments for the developed water hydraulic axial piston pump assembled with two different flanges have been conducted at a water hydraulic component test rig. The experimental results revealed that the volumetric efficiency and noise characteristics of the pump are remarkably improved when the sliding bearing work under hydrodynamic lubrication condition in comparison with dry lubrication condition. The research results have laid the foundation for the development and improvement of the water hydraulic axial piston pump.