Abstract: Fuzzy logic and sliding mode theory are applied to control a nonlinear, complex electro-hydraulic system with large moment of inertia of load. Fuzzy logic is used to obtain equivalent control signal after system states reaching sliding manifold. As a result, chattering caused by switching action is effectively weakened, and external disturbance is restrained also. In order to design a good fuzzy controller without professional experience, membership functions of then-part and control rules are optimized by means of genetic algorithm simultaneously. Simulation result shows the proposed controller exhibits excellent performance and satisfies control demand of the system adequately.