Abstract: Taking Poyang Lake as an example,numerical simulation and remote sensing are fully taken advantage of to monitor the water extend change.Water extend extracted from MODIS images is used to initialize numerical simulation boundaries of water body and calibrate simulation parameters,and also used to be compared with the simulated water extend.With this method,the water extend dynamic change of Poyang Lake from July 8,2001 to November 30,2001 is simulated.Results show that the average absolute error of simulated water level is less than 15 cm.Water extend of numerical simulated and extracted from the MODIS cloud-free images have a good agreement,and the average relative error of water area is 5.7%.This study shows that by making use of satellite remote sensing data,precision of water extend hydrodynamic numerical simulation of the Poyang Lake can be increased.This method can make up for the deficiency of water dynamic monitoring by optical remote sensing in bad weather conditions,thus providing a powerful technique support for water environment monitoring of lakes.