Gas-gas heater (GGH) is applied widely in the desulfurization system of large thermal power plant. There are some problems during the operation process of GGH, such as scale and plugging, poor heat transfer efficiency, much higher operating pressure difference than the design value, and so on, which seriously affect the safe operation of boilers. According to the scaling situation, this paper developed a special cleaning agent for HB-I GGH, and design the specific cleaning process, whose application had a good effect in a power plant in Anhui. The result shows that the cleaning agent has higher economic and safety benefits.