Abstract: Steel plate–UHPC(ultra-high-performance concrete) composite slabs are increasingly designed to be thinner and lighter, making their punching shear resistance under wheel loads a critical design concern. In this study, central loading tests were conducted on six full-scale specimens simply supported along all four edges. The specimens included three flat steel plate–UHPC composite slabs with an 85 mm-thick UHPC layer, two reinforced UHPC slabs with a thickness of 85 mm, and one reinforced UHPC slab with a thickness of 75 mm. In the combination with the research team’s previous experimental results on flat steel plate–UHPC composite slabs, investigated were the effects of UHPC strength, of slab thickness, of punching shear span-to-depth ratio, and of reinforcement mesh position on the punching shear performance of the slabs. The failure modes, deflection development, and strain distributions of the specimens were systematically analyzed, and a calculation method for the ultimate punching shear capacity of UHPC slabs was proposed. The experimental results indicate that: the 75 mm-thick reinforced UHPC bridge deck and the composite bridge deck consisting of an 8 mm-thick flat steel plate and an 85 mm-thick UHPC layer connected by PBL connectors have considerable punching shear capacity reserves under vehicle wheel loads, with capacities exceeding the wheel load by more than 3.2 and 11.2 times, respectively; therefore, punching shear does not control the design; regardless of whether the UHPC compressive strength is 186.8 MPa or 121.92 MPa, both the flat steel plate–UHPC composite slabs and the reinforced UHPC slabs exhibit brittle punching shear failure, while the reinforcing bars and steel plates remain within the linear elastic range at punching failure; the flat steel plate–UHPC composite slabs exhibit three loading stages, namely the bending-dominated stage, the punching failure and structural system transition stage, and the suspension-action-dominated stage, whereas the reinforced UHPC slabs exhibit two stages, namely the bending-dominated stage and the punching failure stage; increasing the slab thickness, reducing the punching shear span-to-depth ratio, increasing the UHPC strength, and relocating the reinforcement mesh from the compression zone to the tension zone are all beneficial for improving the punching shear capacity of UHPC slabs; and the mean ratio of the calculated punching shear capacities obtained using the formula proposed to the experimental values is 1.01, with a small standard deviation and coefficient of variation, indicating a good agreement between the calculation method proposed and the experimental results.