With the aim to reveal the characteristics and influence factors of time response for the magnetorheological (MR) speed regulating start process, the basic component and working principle of the MR speed regulating start control system were analyzed at first. Then, the mathematical control model of output speed was established in combination with the basic laws of magnetic circuit, constitutive model of MR fluids as well as systematic dynamics equations. Moreover, time response of MR speed regulating start under various excitation currents, input speed and load torques was simulated and analyzed by using the Matlab/Simulink software. And subsequently, several speed regulating start experiments were carried out under different initial conditions. Both the simulation and experimental results concerning the response time of the output speed are presented and discussed in detail. Research results indicate that the response time of MR speed regulating start increases with the decrease of the excitation current and the increase of the load torque, while it exhibits an approximate proportional relationship with the input speed; the influence laws of various factors on time response are basically the same between experiments and simulations, which in return proves the validity of theoretical model and simulation analysis. However, simulation values are relatively smaller for about 036s in compassion with experimental results for not considering the magnetic response of the circuit and the rheological response of the MR fluids. Research results may serve to provide a theoretical reference and experimental basis for the development and practical application of the MR speed control technology.