a new 4-axis machine tool, which is used to relief grind sphere gear hob including spherical hob, elliptic hob and arc surface hob, is developed. The principle of machining of spherical hob is introduced first. Transmitting system, numerical system and some key techniques are then introduced. The machine tool can be reconfigured when machining of arc worms and spatial cams beside of machining spherical hob. Four forms of the machine tool for machining different workpiece are also introduced.