Abstract: To address the problem of clutch drag across a broad speed domain, a low-speed drag torque model considering the effects of viscous friction in both fully lubricated and oil film rupture regions of the clearance between friction pairs was developed. Subsequently, a fluid-structure interaction dynamic model of friction plates was established by incorporating elastic and damping forces/torques in the clearance flow field, as well as the collision forces, unbalanced centrifugal moments, and gyroscopic moments acting on the friction plates. By solving this model, collision forces and resulting friction torques at high speeds were determined, forming a method for evaluating impact-induced drag torque under high-speed conditions. On this basis, a unified drag torque model applicable across a wide speed range was proposed, combining both viscous drag torque and impact-induced drag torque. Finally, simulation and experimental studies were conducted to investigate the characteristics of drag torque in wet clutches over a wide speed range. The results show that the drag torque exhibits a non-monotonic trend with increasing speed: it first increases, then decreases, and subsequently rises again. Furthermore, the peak viscous drag torque decreases with higher lubricant temperatures, lower lubrication flow rates, or larger initial clearances between friction pairs, and the operating speed at which the peak drag torque occurs shifts to a lower value under these conditions.