Redundant gears should be eliminated in the design of automatic transmissions in order to reduce inertial power loss and manufacturing costs. The purpose of this paper is to develop a computerized method for the analysis of redundant gears in planetary gear trains. Based on the concept of fundamental circuits, the existence criterion for redundant gears in a planetary gear train is deduced. As a result, an interactive computer program has been developed for the automatic analysis of redundant gears in planetary gear trains. The result of this study is of benefit to the design of automatic transmissions for automobiles.