Continuous contact force model is built in order to investigate joint clearance effects on the dynamics of two-axis hydraulic vibration test system. Test system with clearance joint is imported into the software ADAMS for dynamic simulation， and an experimental set-up is designed and built to achieve some experimental validations under the simple harmonic excitation inputs with different phase, results indicate that coupling vibration effect between two exciters leads to the apparent fluctuation of steady response of accelerations in the case of certain clearance size and excitations out of phase, meanwhile, rapid increase of peak acceleration happens when the excitation frequency and excitation amplitude increase. Thus, selection of clearance size in revolute joint for two-axis hydraulic vibration test system has a critical role in eliminating the non-linear influence。