This paper introduces the structure,operating principle and design method of a new type of automatic ball adding machine.The machine was designed to catch the ball from the storage box by installing a device in the surface of rotary drum,using laser sensor to make non-contact inspection of the steel ball,and equipped with PLC control touch-screen computer to control and recognize the steel balls smartly.It could remedy some shortcomings of the old ball adding machine such as the balls being likely get stuck in the machine.It makes ball mill have fixed quantities of balls by adding steel balls automatically at fixed times.The design has certain characteristics such as reliable performance,compact structure,flexible installation,high level of intelligence and low power consumption.