In order to analyze the robust stability of π -type inductive power transfer system, a generalized state space averaging (GSSA) model based on frequency domain resolving method was first built. An uncertain model was then represented as a linear dynamic system with perturbation feedback, which took into account the frequency uncertainty by separating the object into nominal part and perturbation part with the method of linear fractional transformation. The μ method based on the structure singular value was used to analyze the effect of frequency perturbation on system stability as well as the maximum perturbation allowed for maintaining system stability. The simulation results have verified the accuracy of the μ theory analyses.