A dynamical simulationbased method was presented for detecting damag e in planetary gear sets. Firstly, a dynamic model of 2KH planetary gear sets is employed to study the detection of damage in the planetary gear sets of a hel icopter by dynamical simulation. Then, a new fault feature based on the spectrum sideband of a residual signal is extracted, which is validated by both simulati o n signal and test data. The results of experiment indicate that the feature is e ffective and has acceptable antiinterference ability in detecting toothchipp ed damage of planetary gear sets.