Based on the assumptions that there is perfect contact at the interface between the brake drum and the lining plates, the friction coefficient is constant, the thermal effect is neglected, and the brake drum is a rigid body, the pressure distributions of drum brakes were studied by using the boundary element method. The constant element is used in the two-dimensional model of the drum brake for simplicity and economy. The friction force versus the effective lift at the actuation edge and the location of the maximum pressure are compared and indicate a good correlation with existing data. The effects of the Young’s modulus of elasticity of the metal shoe, the arc lengths of the metal shoe and lining plate, the location, the thickness, the friction coefficient, the Young’s modulus of elasticity of the lining plate, and the angle of actuation force on the pressure distributions were then studied. By selecting proper values of these parameters, a drum brake can be designed to have a more uniform pressure distribution and a longer life.