Abstract: Based on the principle of the strip method，this paper analyses the response function of pitching and heaving oscillation of trimaran-planing boats，resorting to the mature commercial software，SeaKeeper. The calculation is performed under the assumption of head regular waves，and the prediction results are compared with the experimental results under different traveling speeds. The numerical results are seen to be highly consistent with the field data，and the encounter frequencies are also sufficiently close，which suggests that the strip method is applicable in predicting the motion of trimaran-planing boats in the head regular waves.