Disclosed are a secondary-pressurizing energy-saving water-supply system for a high-rise building and an energy-saving water supply method. The secondary-pressurizing energy-saving water-supply system for the high-rise building comprises a valve, a main water inlet pipe, a mainstream flow sensor, a mainstream pressure sensor, a tee joint, an ejector, an auxiliary pressure sensor, a water pump, a first one-way valve, a control box with a controller, a virtual high-level water tank, a second one-way valve, a first electric adjusting valve, a second electric adjusting valve, an auxiliary flow sensor, a surge tank and a user pipeline which are connected mutually. The structure of the ejector is optimized, the technique of the virtual high-level water-tank is adopted, and the energy-saving water supply method is free in energy input, so that the rate of energy recovery of water in a municipal water pipe network is greatly increased, power consumption of the main pump is reduced by 10-35%, the energy is saved, the stability and security is improved and energy conservation and environmental friendliness are achieved significantly.