Abstract： Aimed at the problem of illogical time critical point and large error of the method of equivalent static loads based on displacement in structural dynamic optimization, an equivalent static loads method based on energy principle was proposed which could identify the critical time of structure by getting the spectral element discrete solution space of the structure dynamic response. The mathematical model of equivalent transformation was proposed based on the energy at the critical time, and the optimum solution of the set of equivalent static load was obtained using the global optimization algorithm. Therefore, the dynamic optimization problem could be transformed into a static structure optimization problem and solved. Finally, the effective and engineering practicability of the proposed method was proven by the effective application of the method in dynamic optimization design of a diesel engine piston oil chamber structure. The results expand the scope of the theory of equivalent static loads, providing a new way for the dynamic response optimization design of a complex structure.