Water hydraulic axial piston motor (WHAPM) is one of the key components in water hydraulic system. It is essential to identify the desired engineering materials and material combinations for improving the WHAPM, which are featured by strong wear and erosion resistance. As the candidate materials of friction pairs in WHAPM, the tribological characteristics of 30 wt% carbon fiber-reinforced PEEK (PEEK + CA30) sliding against 17-4PH precipitation-hardening stainless steel under fresh water lubrication were investigated. The friction experiments were conducted on MCF-10 ring-on-ring test rig. With the help of metallographic microscope, an attempt was made to approach the tribological properties of friction pair. The experimental results showed that the ideal sliding velocity is also about 1 m/s when the applied load is between 200 and 600 N. It can be concluded that the slipper designed based on the principle of residual pressure coefficient bearing with auxiliary supporting area is an effective way to decrease the actual pv value in the prototype of WHAPM. The research outcomes will lay the foundation for the design of key friction pairs in the water hydraulic components and system.