In arid and semi-arid regions such as Iran, groundwater is more important for humans and ecosystems than surface water. Different models of groundwater vulnerability assessment can be used to better manage water resources. The purpose of this study is to evaluate the qualitative vulnerability of groundwater resources in the Birjand Plain aquifer using the DRASTIC model and 7 hydrogeological components. DRASTIC model was also modified by adding a land use component (MDRASTIC) based on Analytical Hierarchy Process (AHP) and Fuzzy Analytic Hierarchy Process (FAHP) methods. After calculating the vulnerability index, the vulnerability of each method was mapped and the final index obtained from each method was classified into 4 different categories. Nitrate concentration was used to confirm the results and to analyze the sensitivity of a single parameter. Sensitivity analysis showed that the groundwater vulnerability is mainly affected by water depth and land use. To validate each of the models, their correlation with nitrate concentration was calculated and compared. To determine the correlation coefficient, simple linear regression method was performed and the Pearson and Spearman methods were used. According to the obtained Pearson correlation results, the DRASTIC, MDRASTIC, MDRASTIC-AHP, and MDRASTIC-FAHP models resulted in values of 0.550, 0.680, 0.778, and 0.794respectively. The results show a good correlation between the modified DRASTIC-FAHP model and nitrate concentration as an indicator of groundwater pollution.