The embodiment of the invention provides a method, device and system for injecting water for a water tank and a mobile single machine and belongs to the technical field of engineering. The method comprises the steps that in the situation that the water tank is in need of water injection, whether the water injection condition for injecting water for the water tank is met or not is judged; when thewater injection condition is met, the mobile single machine is controlled to move to a water injection point; when it is determined that a water injection opening of the mobile single machine is aligned with a water injection water pipe of the water injection point, a water injection instruction is transmitted to a water source control module, so that water is injected to the water tank under thecontrol of the water source control module; and when water injection for the water tank is required to be stopped or the continuous water injection time for the water tank exceeds the preset time, a water injection stopping instruction is transmitted to the water source control module, so that water injection for the water tank is stopped under the control of the water source control module. In this way, water injection for the water tank is controlled automatically.