In order to study the differences of the calculation methods for the wave force of small-size pile provided in the Chinese,British and American specifications,in view of the characteristics of pile foundation structure in port engineering and the wave conditions in actual projects,we carry out sensitivity analysis of various factors affecting the calculation results through different cases.The results show that in Chinese,British and American specifications,the wave forces of the small-size piles are calculated all by the Morison equation,and the variation rules of the calculation results by three specifications are basically the same.The different wave theory,the value of inertia coeffecient CM,the marine growth and the group-piles effect are major reasons of calculation result difference.