Referring field observation data on tree configurations consisting of coastal forests and invoking knowledge developed in tree morphology, a typical structure of coastal pine trees was determined. The dynamic responses of the tree structuree against sinusoidal wave motions were computed by modeling the tree into a lumped mass system. The temporal variations and spatial distributions of the horizontal displacement and bending stress of the trunk and branch elements were analyzed. Sensibility analyses were conducted by changing the imput parameters such as incident wave height, period and loading weight due to the leaves in the crown part. The obtained results on the maximum bending stresses can be utilized for the damage analysis of the tsunami barrier forests under tsunami attack conditions.