Abstract A theoretical model is presented here for the fine structures in the solar short centimeter radio bursts discovered recently. The three waves resonance interaction can occur when this radio emission, on its way outward through the corona, interacts with a MHD wave in the corona. In this way, a non-linear modulation in the emission flux can be induced. This model can satisfactorily interpret the inverse proportion relation between the emission flux and repetition rates of the fine structures. Moreover, this theoretical model anticipates that the period of modulation is related to the emission frequency, and the modulated amplitude of the fine structures is independent of the radio flux.