ABSTRACT We present an analytical model for the free–free emission at radio wavelengths produced by the interaction of a Coronal Mass Ejection (CME) with the ambient solar wind. Using our previous models, we show that a dense shell bounded by two shock fronts is formed from this interaction, whose dynamical evolution can be calculated based on considerations of the mass and momentum conservation for the shell. This structure undergoes two stages in its dynamical evolution: (1) A first one of constant velocity, when the shell is bounded by two shock fronts, and (2) a second one, in which a one-shock structure (the leading shock) is decelerated. Here, we compute the emission produced by these shocks, and present a comparison with synthetic observations of the 2011 March 7 CME. Our simplified model gives a physical insight into the free–free emission produced by shocks of CMEs.