Constant chord height, base tangent length and the span of the rod are the parameters describing the tooth thickness of the gear. This article discusses the characteristics of the three tooth thickness parameters, and analyzes the increment relationship of the three parameters. Then, the calculation formula for the conversion between the three parameters increment was derived. Finally, the examples for the formulas were applied. Based on the conversion relationship of the three tooth thickness parameters, the increment of two tooth thickness parameters can be easily obtained once one of the tooth thickness parameters is given. It will be convenient for engineering applications.