The present invention provides a structure for controlling the temperature of hot- water supply from a waste heat recovery system using a three-way valve, comprising: a hot-water tank for storing hot water, the heat of which has been exchanged by a waste heat heat exchanger, the hot-water tank comprising the waste heat heat exchanger for recovering waste heat from a waste heat source and generating hot water, a heating heat exchanger for exchanging heat so as to provide heating using the hot water, and a temperature sensor for checking the temperature of the hot water; a boiler for heating the hot water, the heat of which has been exchanged by the hot-water tank, until the set temperature for heating and hot water supply set by a user is reached, and for supplying same to the spaces to be heated and supplied with hot water; a three-way valve which is disposed on a hot water line entering the boiler from the hot-water tank and can selectively supply, to the boiler, the hot water flowing in from the hot-water tank or water fed directly from a water main; and a control unit for controlling the three-way valve so as to cut off the hot water flowing in from the hot-water tank by using the temperature sensor in case the temperature of the hot- water tank is 0 DEG C to 10 DEG C lower compared with than the set temperature for hot- water supply of the boiler and to supply the water fed directly from a water main to the boiler.