Taken a small-sized unmanned catamaran used for offshore monitoring as an example, the model of the catamaran is established. By two dimensional slice method based on plane potential flow theory, the motion response of the catamaran with different layout schemes is calculated and analyzed. The relationship between layout scheme and the motion performance is obtained. The results show that the draft and inertia moment of the catamaran have obvious effects on motion performance of the catamaran in waves, and should be selected in a certain range. The height of center of gravity has little effect on the motion performance of the catamaran in waves, and the stability should be the main factor considered in design.