The exist researches of the magneto-rheological semi-active suspension(MSAS) control mainly focus on the design of control laws,which aim at obtaining an optimal control strategy to improve the ride comfort and handling stability.In the controller design,the stability of the MSAS system cannot be confirmed owing to the control input time delay considered little.In this paper,a quarter vehicle MSAS model with time-delay is built.Therefore,through formulating the sprung mass acceleration suitably as the optimization object,suspension deflection and tyre dynamic load and coulomb damping force as the constraint objects,with considering the control input time-delay,a delay-dependent state feedback H2/H∞ controller is designed.According to Lyapunov-Krasovskii functional theory,the sufficient conditions for asymptotic stability and the existence of delay-dependent H2/H∞ controller are obtained,and the controller design is transformed into the minimization problem for linear function through linear matrix inequality(LMI).Random road excitation simulations and experiments are carried out.The simulation and experiment results show that the design can preserve the closed-loop stability and achieve the performances for MSAS system in spite of the existence of the control input time-delay.The present study can provide an important basis and method for research on time-delay problem in MSAS and other chassis subsystems.. The exist researches of the magneto-rheological semi-active suspension (MSAS) control mainly focus on the design of control laws, which aims to obtain an optimal control strategy to improve the ride comfort and handling stability. In the controller design, the stability of the MSAS system can not be confirmed due to the control input time delay considered slightly in this paper, a quarter vehicle MSAS model with time-delay is built. Herefore, through formulating the sprung mass acceleration appropriate as the optimization object, suspension deflection and tire dynamic load and coulomb damping force as the constraint objects, with considering the control input time-delay, a delay-dependent state feedback H2 / H∞ controller is designed. According to Lyapunov-Krasovskii functional theory, the sufficient conditions for asymptotic stability and the existence of delay-dependent H2 / H∞ controller are obtained, and the controller design is transformed into minimization problem for linear function throu gh linear matrix inequality (LMI). Rodom road excitation simulations and experiments are carried out. The simulation and experiment results show that the design can preserve the closed-loop stability and achieve the performance for MSAS system in spite of the existence of the control input time-delay. The present study can provide an important basis and method for research on time-delay problem in MSAS and other chassis subsystems.