A relay-heating type water heater, comprising a main internal container (1), a controller and an auxiliary internal container (3), wherein a water inlet pipe (2) is disposed on the main internal container (1), and a water outlet of the lower part of the water inlet pipe (2) is in communication with the internal lower part of the main internal container (1); a boiled water outlet pipe (4) is disposed on the auxiliary internal container (3), and a water inlet of the boiled water outlet pipe (4) is in communication with the inner part of the auxiliary internal container (3); the inner part of the auxiliary internal container (3) is in communication with the inner part of the main internal container (1) by means of a connecting water pipe (31), and a water inlet (311) of the connecting water pipe (31) is located on the internal upper part of the main internal container (1); a first electric heating pipe (5) is disposed inside of the main internal container (1) or at the external bottom part of the main internal container (1), and a second electric heating pipe (6) is disposed inside of the auxiliary internal container (3); the controller controls the first electric heating pipe (5) to heat the water temperature in the main internal container (1) to a set temperature, wherein the set temperature is less than or equal to 90°C. While water is discharged from the boiled water outlet pipe (4), the controller is connected to the power supply of the second electric heating pipe (6) to carry out heating; and when the boiled water outlet pipe (4) stops discharging water, the controller cuts off the power supply of the second electric heating pipe (6) to stop heating.