A crawler system has the potential to expand research and development on seafloors with irregular steep terrain and sand. Characteristic parameters in water, such as added mass, buoyancy, and hydrodynamic forces, considerably affect and decrease the mobility of crawler-type remotely operated vehicles (ROVs). To study and evaluate the mobile performance of a crawler system, it is important to investigate the dynamic motion of the crawler system by considering these effects. This paper presents a mathematical model of an underwater crawler system to show the dynamic effects on the vehicle's motion; experiments were conducted on a crawler-type ROV climbing over a bump in a water tank to examine the slip characteristics at sea. The simulated results agreed well with the experimental results. The mathematical model presented in this paper simulates the dynamic motion for climbing over a bump and the slip characteristics very well, and it reveals the physics of the crawler-type ROV's motion. The proposed mathematical model is useful for dynamic analysis.