In order to solve the problem of difficult control of rebound and large impact during the berthing process of vessels not under command, a variable throttling active buffer method is proposed. The principle of the variable throttling active buffer for vessels not under command has been designed. A mathematical model of the system is established. A simulation model of the system is built based on AMESim. The simulation results of the passive buffer system and the active variable throttle system are then compared. The effectiveness of the variable throttle active buffer system is verified. The main analysis focuses on the pressure in the variable throttle chamber, the displacement of the ship berthing buffer and the speed. The influence of the opening pressure of the variable throttle valve and the overflow valve on the performance of the active variable throttle buffer is studied. The results show that, when using the berthing variable throttle active buffer system, the vessel decelerates smoothly without rebound during the berthing process and there is no pressure impact or fluctuation in the variable throttle chamber. Increasing the variable throttle opening prolongs the pressure response time of the variable throttle chamber. Increasing the relief valve opening pressure prolongs the pressure attenuation time of the variable throttle chamber. Under low-normal speed or light load berthing conditions, the ship berthing buffer decelerates gently.