A table tennis ball service machine includes a ball-collecting unit, a control valve and a ball service mechanism. The ball-collecting unit has a ball-collecting groove connected with ping pong table and having its rear side provided with a blocking net and its lower side connected with a ball-collecting tube and a ball-feeding tube. The control valve is positioned at the lower end of the ball-collecting tube for controlling dropping of balls. The ball service mechanism connected with the upper side of the ball-feeding tube includes a ball service tube, a blower, a support frame, a universal joint, a cam and a motor. The ball serving tube has its outer end extending through the blocking net and formed with an outlet and its rear side formed with an inlet communicating with the ball-feeding tube. Thus, the ball serving speed and the angle can be controlled.