The optical principles of NOAA and TM satellite monitoring flood are explained, and taking Heishan and Taian counties (Liaoning Province) as examples, the NOAA/AVHRR data in flood monitoring are corrected and analyzed in precision by means of the high spatial resolution of Landsat TM data. The average relative error is 4.4%. The results indicate that it is an effective and feasible method in improving the precision of NOAA/AVHRR flood monitoring using TM data.