This paper investigates the meshing behavior of the roller screw, a mechanical transmission device characterized by threaded rollers that transfer a load between the nut and the screw, by analyzing the meshing characteristics between screw and rollers. This study seeks to establish a more accurate mathematical model for the thread surface by creating a modeling process in which the max radiuses of the threads are calculated more precisely. The contact line distribution and the contact location were also calculated in order to confirm the cross section of the meshing points. In the research presented in this paper, the actual transmission ratio is analyzed and the study results in a new method to calculate the actual transmission ratio. In this study, the helical angle and the vertex angle are proven to be of great significance after a careful analysis of their influence is conducted.