The efficient hot-water system of multi-energy cascading utilization is able to effectively utilize solar energy (the solar energy is used as the priority to produce hot water during the day when solar illumination is high), peak and valley electric price difference (during the night, the heat pump water heater is switched on to produce hot water, which will be stored in the heat storage water tank), air energy (in summer and the transition season, the high-grade thermal energy in the air is utilized to produce hot water) and sewage heat energy (the sewage source heat pump is switched on first to utilize the high-grade thermal energy in the sewage to produce hot water). The efficient hot-water system can also be used to substitute traditional boil burning boiler and gas-fired boiler, with satisfactory economic benefit. It can be extensively applied to public building (such as domestic hot water, floor heating hot water and swimming pool hot water) and industrial building (constant-temperature production process water).