Abstract: High speed trimarans，with their excellent performance in drag reduction，sea-keeping and stability，have wide application outlook in both military and civil markets. Despite the fact that high speed trimarans have already been widely applied globally，their wave-making resistance forecast，a key factor in the design process，have not been so rigorously investigated. This paper employs the tent function to design the demihull structure of high speed trimarans，through which a variety of ship form parameters are calculated. Moreover，the improved linear wave-making resistance calculation algorithm is adopted，and the obtained results for high speed trimarans are compared with model test results，which validate the proposed method in the preliminary design stage.