This article briefly introduces the structure of the tooth shape silence chain. The touch point of the roll pins separate when the chain goes around the sprocket gear. It deduces the dimensions of the offset angle α and the roll pin angle θ with mathematics method. This preface shows when the outer circular arc R≈0.5P, the fluctuation of the chain transmission speed is the least. When R＝0.5P, We deduce the size of the roll pin by the value of α、θ、R and the ultimate tensile strength, then we can get the structure parameter of the chain plate hole by the method of geometrical construction.