Due to the presence of amplitude and phase errors in airborne weather radar, the performance of clutter suppression is reduced, and the estimation of low-altitude wind-shear wind speed is not accurate. Considering these problems, this paper presents a low-altitude wind-shear speed estimation method based on combined space-time main channel adaptive processing (CMCAP). This method first reduces the dimension of the radar echo data of the measured range unit by constructing a dimensionreduced joint space-time transform matrix, and then constructs the optimal weight vector of the dimensionreducing processor to adaptively filter the reduced-dimensional data. Furthermore, accurate estimation of the speed of the wind field is achieved in the presence of amplitude-phase error. Simulation results prove the effectiveness of the proposed method.