To study the coupling vibration between an inerter and a vehicle inerter-spring-damper (ISD) suspension system and its effect on the suspension performances, the inerter-sprung mass coupled coefficient was defined to represent the influence level of the coupling effect between inerter and sprung-mass on the suspension vibration transfer features. Then adopting the transfer function method and the state space method, the models of a 1/4 vehicle suspension in frequency domain and time domain were established, respectively. Using the two models, the influence of the inerter-sprung mass coupled coefficient on the suspension performance was simulated and analyzed. Simulation results indicated that compared with the conventional passive suspension with the same stiffness, increase in the inerter-sprung mass coupled coefficient  can effectively improve the vibration transfer amplitude-frequency characteristics of body acceleration, suspension dynamic stroke and tire dynamic load at a lower frequency resonance; their amplitude-frequency peaks are reduced by45.94%, 37.5% and 51.11%, respectively; meanwhile, the root-mean-square values of body acceleration, suspension dynamic stroke and tire dynamic load are reduced by5.41%, 36.36% and 6.19%, respectively to effectively improve the ride comfort of a vehicle.