according to the relative motion between components being plane motion or spatial motion, it can be classfied into plane connecting rod mechanism and spatial connecting rod mechanism.According to the number of components in the mechanism, it can be classfied into four-rod mechanism,five-rod mechanism etc.. Normally,the connecting rod mechanism of five rods and over five rods is named as multi-rod mechanism. When the degree of the connecting rod is 1, it is named as single freedom connecting mechanism; When the degree of the freedom of connecting rod is greater than 1,it is named as multiple freedom connecting rod mechanism. According to the kinematic chain of the connecting rod machanism being open chain or closed chain , it can be classfied into open chain connecting rod mechanism (mainpulator is normally a spatial open chain connecting roe machanism with its kinematic pair being revolute pair of sliding pair ) and closed chain connecting rod mechanism. As the components of plane connecting rod mechanism with single closed loop are at least numbered 4, so the simplest plane closed chain connecting rod mechanism is four-rod mechanism. Other multiple rod closed chain mechanism is only to increase rods on that basis ;as the number of the components of spatia connecting rod mechanism with single closed loop is at least 3,so it can be spatial thrree-rod mechanism composed of three components.