Parameters of induction motors have crucial effects on power system simulation. This paper proposes a dynamic aggregation method of induction motors. In this method, firstly, starting off the electromechanical models of induction motors, taking the coefficients of the electromechanical equations and steady state slips of motors as the characteristic vectors, motors are grouped with fuzzy C-means clustering method. Then, electromechanical equations of the equivalent motor are obtained by averaging that of the individual motors in the same group. Finally, parameters of equivalent motors are calculated based on the relationship of transient impedance before and after aggregation, and the principle that active and reactive power loads are equal before and after aggregation. Simulation results show that the proposed method can improve the precision of simulation