Groundwater vulnerability assessment coupling with geographic information systems (GIS) should be considered as an important means for groundwater management, especially in agricultural areas. Nowadays, for groundwater vulnerability evaluating, DRASTIC model has been very popular and widely used in the world. However, DRASTIC model has some disadvantage. To overcome the problem, this paper proposed a modified DRASTIC model based on entropy theory and fuzzy theory. Moreover,three additional parameters, were added to the modified DRASTIC model, which were wastewater discharge of unit area, fertilizer usage of unit area, and density of river network. Using ArcGIS10.2 and the modified model, groundwater vulnerability grade (GVG) in Tianjin plain was analyzed and calculated. Groundwater vulnerability map of the plain area in Tianjin was constructed. According to the results, the study area was divided into five level zones: low vulnerability zone, lower vulnerability zone, medium vulnerability zone, higher vulnerability zone and high vulnerability zone, with coverage area of 17.1%, 26.7%, 25.2%, 22% and 9%, respectively. The results are consistent with the actual situation of studied area.