There are many different forms of twin screw extruders. The main difference is that the rotation direction and the meshing degree of the screw are different. According to the relative position of two screws, twin-screw extruders can be divided into meshing type and non meshing type. In meshing twin screw extruders, according to the degree of engagement, they can be divided into partial meshing type and complete meshing type. According to the rotation direction of the screw, it can be divided into the same direction rotation and the heterdirectional rotation, and the hetero rotation is divided into two kinds: inward and outward. It can be divided into parallel twin-screw and conical twin screw, which is intersected by two screw axes or parallel. The relationship between the steering and meshing of a twin screw extruder is illustrated as the picture show.