Gear trains have the advantages of high speed reduction and capability of differential drive, so they are the often used in transmission systems. In this paper, a graph representation and a matrix representation are proposed to represent the kinematic structure of the gear trains. These representtations are based on graph theory and the methodology of fundamental circuits for gear trains. Finally, a systematic method is further developed for the analysis of the kinematics and static of general gear trains. The results of this work are used as a tool to design the general gear trains.