In response to the need for high timeliness and accuracy monitoring for inundation region during flood disaster, a new extraction method of water areas based on SAR texture and LightGBM was proposed. Compared with other methods, such as the SDWI water index, SVM, RF and GBDT methods, it shows that the accuracy of water extraction of river, lake and flooded area is beyond 98% and higher than other methods. Meanwhile, the operating efficiency of the proposed method is 20 ~ 100 times higher than other methods, which greatly improves the timeliness of inundation emergency monitoring during flood disaster.