Compared with their metal counterparts, the insufficient erosion resistance of polymer matrix composites (PMC) is a key issue for application in aero-engines. In this study, multilayered coatings were deposited on carbon fiber reinforced bismaleimide polymer composites using detonation spraying to improve their erosion resistance. The coatings consisted of a polymer–aluminum mixed transition layer, pure aluminum bond layer, and WC-17Co top layer The microstructure and bond strength of the coatings were characterized by using scanning electron/transmission electron microscopy and mechanical testing, respectively. Furthermore, solid particle erosion tests were conducted on coated and uncoated PMC at 25 and 250 °C using an air jet. The tests showed that the coatings 150 µm thick were well bonded to the PMC substrate. Substantial enhancement of the coating adhesion up to 16.5 ± 0.5 MPa was achieved by the optimization of the polymer–aluminum mixed transition layer. Under the same erosion conditions, the volume loss of the coated PMC was less than 1/10 of that of uncoated PMC, indicating the effectiveness of the coating to prevent the PMC from the foreign objects’ impact damage. Finally, the coating erosion mechanisms are discussed.