Abstract: Flood monitoring and estimation is one of the main tasks of crop condition monitoring. This paper worked over the macroscopical and fast monitoring method of flood hazard over large area using NOAA AVHRR image,including the discriminating arithmetic design of flood water based on the typical spectrum characteristic,and the flood area statistic based on the integration with GIS and background database. A monitoring test was carried out on the super flood hazard of the Changjiang River region in 1998 with a preferable result.