Abstract: The calculative analysis for driving contact process of tooth surfaces of Spiral bevel and hypoid gear by use of electronic digital computer is an advanced technique in recent times. It can give the decisive criterion to collect best parameters of gear cutting adjustment and design. M. L. Baxter introduced this method first[2], and called it"Tooth surfaces contact analysis(TCA)".This paper discribes the mathematical procedures in wuich each item of formulas in the "TCA" derives as well as the conjugate action principle of these calcultion in any part; presents the fundamental formulas to calculate tooth bearing, Y-H adjustment values and motion graph.