One hydraulic ball joint with variable stiffness characteristics for rail vehicles was proposed, which used hydraulic mechanism embedded in rubber elastomer to improve dynamic stiffness. The implementation principle of the variable stiffness characteristics was introduced, and the frequency dependence, amplitude dependence and pre-load dependence of hydraulic ball joint was mainly experimental researched. The test results showed that this hydraulic ball joint can achieve low stiffness at low frequency and high stiffness at high frequency, and this property is strongly related to excitation amplitude and pre-load. The structural scheme and research findings are of great significance to guide the engineering application of the liquid rubber composite vibration damping technology on rail vehicles.