The invention provides a heat-pump water heater and an adjusting method thereof. The heat-pump water heater comprises a main loop, a liquid storage device, a first branch, a second branch and a third branch. The main loop comprises a compressor, a first heat exchanger, a throttling device, a second heat exchanger and a gas-liquid separator, and the compressor, the first heat exchanger, the throttling device, the second heat exchanger and the gas-liquid separator are connected sequentially in series. The liquid storage device is connected to a first pipeline section through the first branch, the first pipeline section is located between an exhaust outlet of the compressor and the first heat exchanger, and a pressure increasing valve is arranged on the first branch. The liquid storage is connected to a second pipeline section through the second branch, the second pipeline section is located between an inlet of the gas-liquid separator and the second heat exchanger, and a pressure reducing valve is arranged on the second branch. The liquid storage device is connected to a third pipeline section through the third branch, and a flow regulating valve is arranged on the third branch. By means of the eat-pump water heater and the adjusting method thereof, the problem that a heat-pump water heater cannot effectively adjust the refrigerant amount in a system when the operating condition of the system changes in the prior art is solved.