A larger frequency fluctuation will be caused when fault occurs in the power systems where the grid structure is relatively weak or isolated islands are formed after system splitting in asynchronous networking system. In this case, it is was very important to consider the frequency characteristics of the induction motor when it is modeled. Based on the first order of mechanical transient model of the induction motor, the expression of steady and dynamic state slip ratio of the system frequency under different load characteristics by analytical method was deduced. On this basis, the absorbed active power and reactive power were derived, and then the powerfrequency characteristics of the induction motor were analyzed. The fifthorder electromagnetic transient simulation model of induction motor was established in MATLAB simulation software to simulate and analyze the powerfrequency characteristics of induction motors with different load characteristics. The simulation result was consistent with the theoretical derivation, so it was correct and effective to deduce the frequency characteristics of an induction motor under the simplified model.