In this paper, a position control method based on an improved dynamic surface control is proposed for an underactuated underwater biomimetic vehicle-manipulator system (UBVMS) driven by undulatory fin propulsors. A surge force adaptive process is designed to solve the underactuated problem of the UBVMS. And the proposed closed-loop control system is verified to be stable in terms of Lyapunov theory. Simulation results indicate that the proposed control method has good control effectiveness. Finally, experiments in an indoor experiment pool are implemented to validate the control method's feasibility and robustness in the applications of UBVMSs.