The electricity consumption of axial IDF and FGD booster fan in 300 MW units of a Henan power plant was huge. To gain the best energy-saving retrofit scheme, the necessary of retrofit was confirmed by analyzing the operation characteristics and operation optimization test. The IDF and FGD booster fan energy-saving estimate of some scheme was carried out by fan operation characteristics test. By analyzing technical economic, difficulty and reliability, frequency conversion retrofit for IDF was fixed to be the best scheme. FGD booster fan was suggested not to retrofit. This scheme has finer energy-saving effect, and the difference between the estimate value and real value of energy-saving is very small. The energy saving estimate, based on operation characteristic test, is quite accurate and can avoid some unfavorable situations possibly occurred in frequency conversion retrofit.