To investigate the bearing mechanism of modified clothoid (MCL)-shaped composite dowel shear connectors and the influence laws of various factors on their shear bearing capacity, the stress states and failure modes of the steel dowel, concrete dowel, and transverse through-reinforcement that constitute the MCL-shaped shear connector were deeply analyzed in this paper based on an experimentally validated finite element model. Furthermore, the influence laws of transverse through-reinforcement, steel dowel thickness, and concrete strength on the shear bearing capacity of the MCL-shaped composite dowel were explored. The research results indicate that the bearing process of the MCL-shaped composite dowel exhibits elastic, elastoplastic, and failure stages. When the MCL-shaped composite dowel reaches its ultimate bearing capacity, the concrete dowel is severely damaged, dominated by shear failure; the steel dowel is in a compressive-shear state and locally enters a plastic state. Compared to the lower transverse through-reinforcement far from the shear action end, the upper transverse through-reinforcement is significantly deformed and serves as the primary source of ductility for the concrete dowel. Increasing the concrete strength can enhance the shear bearing capacity of the MCL-shaped composite dowel and delay the development of splitting cracks and prying failure. A larger diameter of the transverse through-reinforcement leads to a stronger shear resistance capacity. The thickness of the steel dowel significantly affects the shear performance of the MCL-shaped composite dowel, determining whether the shear bearing capacity of the MCL-shaped composite dowel is controlled by steel dowel failure or concrete shear failure.