In the ocean, there exist not only free short waves that satisfy the dispersion relation, but also short waves that are generated by the breaking of the mesoscale waves. Microwave electromagnetic waves undergo Bragg scattering with both the aforementioned two types of short waves. To verify the echo Doppler characteristics of these broken short waves, a composite sea surface scattering model for X-band Doppler radar was constructed, which considers the mutual coupling of free waves, broken short waves, and gravity waves on the sea surface. Under this model, the echo Doppler spectra were studied under different incident angles, wind speeds, and directions. It is shown that the existence of broken short waves effectively explains the asymmetry of the echo Doppler spectra observed by radar at moderate incident angles and grazing angles, as well as under upwind and downwind conditions. The influence mechanism of sea surface fluctuations on radar scattering characteristics is further revealed through the analysis of echoes under different conditions. Important theoretical support for the scattering mechanism of coherent microwave radar on composite sea surfaces is provided by the research findings.