Based on the principle of precise integration method, for DOF and MDOF system, it is supposed that external loads are in linear regular within small discrete time. In further, a identification method of dynamic loads are proposed. And two real ice loads are used to study the new method. The results of numerical examples indicate that the precise integration method, with better steady and capability of resisting noise, are applicable for both steady or random loads. Otherwise, it can save more time for calculation and can be applied in real engineering.