The inverted recirculating planetary roller screw mechanism is a novel transmission screw that enables integrated nut-motor design, simplified fabrication, high load capacity and long service life. The nut engages with multiple annular-grooved rollers, which further mesh with the screw threads to transmit power. This paper first proposes an innovative structural design of the inverted recirculating planetary roller screw mechanism, derives the dimensional range of the screw’s unthreaded section, establishes the parameter matching equations for the mechanism components, and performs a virtual modeling. Next, the calculation formulas of the motion parameters of the inverted recirculating planetary roller screw mechanism are derived. Then, a dynamic simulation model is developed using ADAMS software, and the results are compared with the theoretical ones, with a relative error ranging from 0.25% to 1.12% being obtained, which validates the feasibility of both the simulation approach adopted in this study and the proposed mechanism. Finally, the variation patterns of the thread contact force as well as the collision force between the rollers and the boss slope in the inverted recirculating planetary roller screw mechanism are quantitatively analyzed from two aspects: the operating condition parameters and the inclination angle of boss inclined plane. It is found that the axial contact force in the threaded section is minimally affected by the rotational speed and the boss inclination angle, but is significantly influenced by the external load; that the average axial contact force increases markedly with the external load; and that the collision force between the rollers and the cam ring boss slope increases with the increase of nut’s rotational speed and screw load, but decreases significantly with the increase of boss inclination angle. The research results of this paper provide certain reference for optimizing the design of the inverted recirculating planetary roller screw mechanism.