A heat pump type water heating unit based on peak and off-peak power consumption, a control method therefor and a control system thereof. The control method comprises the following steps: an off-peak electricity signal determining step: determining whether an off-peak electricity signal is inputted, and if yes, performing the start controlling step for a heat pump and a secondary thermoelectric device, if not, controlling the operation of the heat pump type water heating unit in a normal way; and the start controlling step for the heat pump and the secondary thermoelectric device: controlling the heat pump and the secondary thermoelectric device to start, according to value comparison between a current water tank temperature T5 and a water tank setting temperature Ts and between the current water tank temperature T5 and a secondary thermoelectric device starting temperature T5start. The heat pump and the secondary thermoelectric device are controlled to start by determining whether an off-peak electricity sig
