Abstract: Ship collision is a complex process consisted of non-linear instantaneous responses. After the collision occurs，the components within the collision zone will rapidly enter a plastic flowing state which entirely disables the components in formats of tearing and buckling. In this paper，the problem concerning small fast boat collisions was presented with its crashworthiness characteristics being discussed. Firstly， the progressive failure of stiffened side plates colliding with a bow was described，and the corresponding penetration depth was analyzed. Next，a crashworthiness evaluation model was established for small boat structures by considering their plastic strain criterion and the penetration depth criterion comprehensively. Finally，the numerical simulation was conducted using finite element analysis，and the optimization procedure for crashworthiness of an innovative side structure was investigated. The results show that for small fast boats，the collision damage mainly comes from the overall deformation of the hull，whose region occupies a large proportion of the boat. In brief，using plastic strain and penetration depth as criterion is both feasible and effective in crashworthiness evaluation tests.