Differential uncertainty is involved in actual system inevitably. That brings great inconvenience for the controller design. In this paper we treat the differential uncertainty as a separate item, and use the robust control theory to analyze the robust performance. Considering the impact of parameter variations, un-model dynamics and external disturbances, we design robust H2/H8 controller. We use the ship yaw/roll coupling system to verify the effectiveness of the controller. We present a simulation result which shows that the robust H2/H8 controller designed in this paper has good robust stability and can meet the system required performance.