Abstract: To study the relationship between the design variables and the pressure angle of cycloid-pin gear transmission mechanism, the pressure angle between the cycloidal gear and the pin tooth and its influencing factors were analyzed. The mathematical model of the cycloidal gear was established using the conjugate theory. According to the characteristics of multi-teeth meshing in the cycloid-pin gear transmission mechanism, the expression of the pressure angle was derived, and the meshing state between the cycloidal gear and the pin tooth was simulated. By applying VC++ and AutoCAD software for calculation and simulation, the cycloid-pin gear mechanism of the RV reducer used in the industrial robot joints was applied as an example to clarify the influence of design variables on the pressure angle, such as eccentricity, radius of the pin position and the radius of the pin tooth. Based on the meshing simulation between the cycloidal gear and the pin tooth, the cause of the influence on the pressure angle was revealed. Results show that eccentricity has a great effect on the pressure angle, the radius of the pin tooth position is moderate, and the effect of the radius of pin tooth can be neglected. The research provides a theoretical basis for the parameter design and analysis of cycloid-pin gear mechanism.