Abstract: The national environmental protection authority requires that the large FGD bypass shall be removed from thermal power generation projects. In the FGD system of one 350-MW supercritical unit with single booster-fan, the boiler will be forced to shut down due to the boiler main fuel trip(MFT) in the case of booster-fan trip. In order to ensure the unit long-term secure operation and reduce the number of unplanned outages, the original large FGD bypass is removed while a bypass for the booster-fan is built. At the time of booster-fan faults, the booster-fan bypass will be opened quickly and the booster-fan runback(RB) will be triggered simultaneously. Through the improvement of booster-fan control strategy and the successful RB tests at different loads, the unsafe hidden issues in boiler operation are resolved with satisfactory results.