Among water-related disasters, flood is one of the most overwhelming impacts which causes loss of lives and livelihood worldwide. Risk zonation and estimation is a prolonged task which require a multiple factors analysis because always not only a single factor responsible for flood incidence, and it changes with different geographical location. Therefore, flood risk mapping is essential for pre-preparing, managing and mitigating of water-related disaster. The present study was designed to evaluate the efficiency of the geostatistical method i.e., rank sum (RS) along with geospatial techniques to identify potential flood risk areas in Sundarban Delta of India. Thus, primarily, nine possible factors such as rainfall deviation, slope, slope aspect, land use land cover, soil type, clay content in soil, distance from river, river flow direction and catchment area were considered for assessment of flood risk mapping. The task employs two stages of analyses including preparation of thematic layers in geographic information system (GIS) environment and combining with flood causative factors using RS as a geostatistical method. Finally, to fine possible flood risk areas, weighted overlay analysis was performed. The result reveals that rainfall has a great influence on flood in Sundarban with weight of 0.20, concomitantly slope, catchment area, distance from river and flow direction have also an important influence on flood risk with weight of 0.18, 0.16, 0.13 and 0.11, respectively. This analysis finds that the geostatistical analysis is capable of making a correct and consistent prediction for flood extent. So, the rank sum technique integrated with GIS are proposed for evaluating flood risk in other regions of the world.