As a kind of high-performance ship, compared with traditional mono-hull, the side-hull position of a trimaran plays an essential role in the hydrodynamics and motion characteristics, which is more significant for the seakeeping performance of a trimaran in waves of different headings. In this paper, the moving forward of trimaran in waves of various headings was simulated by a hybrid numerical method, which combines the fully nonlinear potential flow theory and viscous flow theory. The numerical method was validated firstly. Then, the trimaran model with two different layouts was obtained by increasing the hull separation and moving the side hulls forward. Finally, the motion of the trimaran with different layouts in waves of various headings was simulated, and the effect of layout on the motion response and added resistance were investigated.