Robust H∞ control can design a good controller of system only contains one perturbed block, however, it still uses the little grain theorem to judge when it conducts the system that contained several perturbed blocks, which makes the results become conservativeness. There are parametric uncertainty and dynamic uncertainty in suspension system. Using robust H∞ control theory to design a controller of semi-active suspension makes the results conservativeness. A way of using the structured singular value μ method to design the controller of the semi-active suspension was proposed. Some perturbed blocks to a diagonal matrix could be integrated, and the conservativeness of the little gain theorem has been overcome. The simulation results showed that the semi-active suspension performances with robust μ control were much better than the suspension with H∞ control.