Abstract: The wave making resistance, the sinkage and trim of trimaran in calm water were iteratively calculated based on the Rankine source panel method. During the process, the NURBS surface was used to express the ship surface, the instantaneous mean wetted surface was calculated according to the preiteratively calculated sinkage and trim, and the fully quadrilateral mesh was generated by the paving method. The comparison between the calculated sinkage and trim and the experimental results indicates that with present method the trimaran sinkage and trim could be calculated very accurately, and the wave making resistance calculation precision could also be enhanced.