Focused on the failure of the brake system of a businessjet,through principle analysis and function hazard analysis to the brake system, two reasons were demonstrated for the failure.One reason was the internal leakage caused by the seal failure of the shuttle valve. In another word, when the brake was released, the different pressure between two ends of the piston inside the shuttle valve lead to its seal failure, resulting in the internal leakage. The other reason was the insufficient braking pressure caused by the lowlyinstalled reservoir. Aiming at the two reasons, an improved brake system was made, which had passed the laboratory test and taxiing test.