In a power plant of 300MW, the power consumption of its axial Induced Draft Fan (IDF) and Flue Gas Desulfurization (FGD) booster fan was high on the whole. So it is necessary to take measures to reduce the power consumption by energy-saving retrofit. Firstly, a series of test and optimization are carried out on its operational performances. Furthermore, several retrofit schemes are worked out. Then, based on a series of test about its operational characters, an evaluation on potential to save energy is carried out for the IDF and the FGD booster fan. Finally, according to the comprehensive analysis including technical economic, difficulty and reliability, it is of the best scheme to carry out the frequency conversion retrofit for IDF. In fact, its effect is good after the retrofit is conducted, namely, the energy-saving index is almost the same as from evaluation. Obviously, the evaluation as for performance test is quite accurate and can avoid several problems likely to occur in frequency conversion retrofit.