Water hydraulic technology is developing rapidly at present. The water hydraulic piston pump has become a key component in the field of water hydraulic technology. The paper describes the invention of a new mechanism which translates rotational movement into linear motion for application in a water hydraulic piston pump. The kinematic and dynamitic models of the mechanism were built and simulation was accomplished based on the mathematic models. Simulation results were analyzed and compared with a traditional swashplate slipper pump. Comparison results indicated that this mechanism could reduce the number of tribology pairs and reaction force between piston and cylinder block. The lateral force was only 1/18 of that for a swashplate slipper piston pump. The value of product between pressure and velocity (PV value) for the piston was small, resulting in a great reduction in friction and wear for the piston–cylinder couples. The new pump was tested in a flow test apparatus. The experimental results showed that the pump achieved a volumetric efficiency of up to 92% at the required flow rate and operating pressure. The pump was found to have steady and excellent operating characteristics. This research contributes to the overall development of water hydraulic technology.