A servo brake cylinder for a distributed brake system with an electric motor, a ball screw assembly with a lead screw and a nut, a piston, a cylinder body is disclosed. The electric motor is connected to the ball screw assembly. The piston is installed in the hollow inner space of the cylinder body, slidable axially. The piston has a hole at the center formed by three sections of surfaces including a first cone surface, a cylindrical surface a second cone surface. One end of the lead screw is connected with the nut, and the other end at the tip of the lead screw has three sections of surfaces including a gradually constricting cone surface from the tip followed by a cylindrical surface, further followed by a gradually expanding cone surface. These surface sections at the lead screw and the three sections of the surfaces at the hole of the piston form an inlet valve and an outlet valve between the piston and the lead screw.