The invention discloses a method for regulating the temperature difference of a water steam system of a gasification furnace through desalted water. The method comprises the following steps of: conveying boiler supply water to a deaerator; performing thermal deaeration and chemical deaeration, and adjusting a pH value; and conveying the water from the deaerator to a boiler through a water pump. The method is characterized in that the boiler supply water is the desalted water; the pH value of the desalted water is 7 to 8; the desalted water is not deoxidized; the temperature is 20 to 30 DEG C. In the process of adjusting the pH value of the desalted water, after the desalted water enters the water steam system of the gasification furnace, drugs are added into a steam pocket while the temperature rises, and the desalted water is forcedly circulated, so that the pH value of the desalted water can be adjusted to be 8.5 to 9.2. According to the method, parts of the gasification furnace can be prevented from being damaged by thermal stress, and good temperature-rise and temperature-drop effects are achieved.