Tanguarhaor, the most diversified ecosystem is not only ecologically but also socio-economic important for supporting livelihood to around 70,000 people. Geographical location has made it vulnerable to adverse impacts by flash flood in almost every year. Our study aims to assess the loss of agricultural land cover due to flash flood occurred on April 2017. We have used 'before' and 'after' satellite images extracted from USGS database to assess the change of land cover in Tanguarhaor basin. Our result shows that a considerable area of agricultural land has been submerged by this flash flood and eventually a significant amount of crop has been lost. Consequently, almost 60 thousand people are at risk to suffer from food insecurity along with scarcity of safe drinking water due to contamination of pathogenic water microbes from unhygienic sanitary condition. Hence, we expect this study will help to visualize the loss of crop production that may play a significant role for ensuring food security in the haor basin of Bangladesh.