To improve ride comfort and stability of vehicle, a kind of semi-active suspension with double pole magnetorheological damper was designed. Based on the analyses of mechanical model for magnetorheological damper, an improved polynomial model of magnetorheological damper was proposed and a dynamic model of semiactive suspension system with magnetorheological damper was established. The physical prototype for magnetorheological damper was made and the mechanical property tests of the magnetorheological damper were completed. The curves of damping forcedisplacement and damping force-speed were acquired. By using the test results, the model parameters were identified and the improved polynomial mechanical model of the magnetorheological damper was verified. Considering the timedelay impact on the suspension system, the critical time-delay for the magnetorheological suspension was calculated. Smith forecasting compensation control strategy was used and the timedelay fuzzy controller of semi-active suspension with magnetorheological damper was designed. The simulations of time-delay compensation control were carried out by Matlab software. And the test bench systems for semiactive suspension were developed. Then, the tests of the semi-active suspension with magnetorheological damper were done. The simulation and experimental results showed that the magnetorheological damper had good energy dissipation effect, good controllability and the maximum of vibration attenuation function. The improved polynomial mechanical model of the magnetorheological damper was correct. Compared with the passive suspension, sprung mass accelerations for magnetorheological semi-active suspension were dropped by about 30%. The damping effect of the developed semi-active suspension was obvious.