The invention provides a ballasting system, a floating dock and a floating dock system. The ballasting system consists of multiple ballasting units; each ballasting unit comprises an injection valve,a discharge valve, a variable-frequency water pump and a suction opening; each injection valve is arranged at a water injection opening; each discharge valve is arranged at a water outlet; each variable-frequency water pump is arranged between the corresponding injection valve and the corresponding discharge valve; and each suction opening is formed in a ballasting water cabin of the floating dock. During movement and loading, an external control station control the injection valves or the discharge valves in the ballasting unit corresponding to the ballasting water cabins to open, corresponding variable-frequency signals are transmitted to the variable-frequency water pumps in the ballasting units corresponding to the ballasting water cabin to control the flow of the ballasting water cabins corresponding to the variable-frequency water pumps, and therefore, the floating dock keeps horizontal in a movement and loading process. The flow control accuracy of the ballasting system of the floating dock can be improved, movement, loading and unloading functions of the floating dock as a water semi-submersible barge can be fulfilled, and the functions of the floating dock are expanded.