On the basis of the unified model, the multi-frequency averaging method is presented and applied to the analysis of the switched converters working on the discontinuous conduct mode. Using the presented method, not only the base wave in a steady state, but also the size of each harmonic can be obtained. The practical simulation indicates that the method is better in logicality, easy in programming and of great precision in computing, furthermore, it is applicable to the steady state solution and the analysis of ripples in the open loop and various kinds of closed loop systems.