The inverted recirculating planetary roller screw mechanism is a novel transmission screw that enables integrated nut–motor design, offering 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, and establishes the parameter matching equations for its components, followed by virtual modeling. Secondly, the calculation formulas for the motion parameters of the inverted recirculating planetary roller screw mechanism are derived. A dynamic simulation model was developed using Adams software, and the results were analyzed. The relative error between the simulation and theoretical results ranged from 0.2% to 1.12%, validating both the simulation approach adopted in this study and the feasibility of the proposed mechanism. Finally, the variation patterns of the thread contact force and the collision force between the rollers and the boss slope in the inverted recirculating planetary roller screw mechanism were quantitatively analyzed from two perspectives: operating condition parameters and the slope angle of the boss. The axial contact force in the threaded section is minimally affected by the rotational speed and the boss slope angle, but is significantly influenced by the external load; the average axial contact force increases markedly with increasing external load. As the nut’s rotational speed and the screw load increase, the collision force between the rollers and the cam ring boss slope also increases. However, as the boss slope angle increases, the range of collision force decreases significantly. This study provides a valuable reference for optimizing the design of the inverted recirculating planetary roller screw mechanism.