At present, the reliability of mechanical structures is based on Failure Mode and Effects Analysis or importance calculation mostly, ignoring the uncertainty of parameters and performance margin. In order to analyze the reliability of the brake device accurately, uncertainty analysis method of the brake device is presented, and the belief reliability of the brake device is calculated basing on the uncertainty mathematical model. Conducting a Failure Mode and Effects Analysis (FMEA) on the brake system, basing on the result of FMEA, the key performance parameters of the brake device are determined to be electromagnetic force and braking time; Basing on key performance parameters, an uncertainty mathematics modeling method for the brake device is proposed. Basing on Taylor expansion, a reliability calculation method is provided for armature mass, armature damping, spring stiffness, armature displacement, and frictional force during the movement of the armature; Taking the brake device as an example, the belief reliability of its shaft rotation angle and electromagnetic force is calculated.