This article deals with the conjugate cam mechanism of the driven rod in roller-plate swinging. Applying the research method of the theory of gear meshing, the authors introduce the interrelated conception of the sphere of gear research to the cam members, hence deeply delineating the essential characters of the conjugate cam and obtaining a series of formulas for accurately calculating some important parameters.The last part of this article presents a necessary theoretical basis for the design, calculation and manufacture of the conjugate cam mechanism.