Abstarct: The study area is Birjand alluvial aquifer which is located at the central part of South Khorasan Province with a total area of 271.2 square kilometers. Birjand city, with a population of about 200,000, is located at the center of the plain and groundwater is the only source for drinking water and agriculture. Therefore, estimating groundwater recharge is essential in order to evaluate and use aquifer in this area. To this end, four methods of water-table fluctuation, chloride mass balance (CMB), isotope and water-budget have been used for estimating recharge. The average hydrograph of the aquifer represents a general decline trend during the 12-year period, decreasing by about 47 centimeters annually. In order to estimate the recharge in the water-table fluctuation method, the specific yield rate was considered using the dominant soil texture in well logs and the results of pumping tests was 6%. The average amount of annual recharge using this method was estimated 9 million cubic meters per year. The values of chloride concentration in groundwater vary from 234 to 2400 mg / L, and in precipitation from 1.7 to 28.4 mg / L. The calculated recharge using the mass-calorie balance was estimated 2.49 million cubic meters. Due to the fact that chloride ion was not stable in the aquifer, its values were not used to estimate recharge. The water-budget for Birjand aquifer with an area of 271.2 sq. Km was calculated for the year 2016-2017. The recharge value of this method was estimated 11.3 million cubic meters. The value of recharge from precipitation in Birjand aquifer using stable isotopes of oxygen 18 and deuterium was estimated between 0.24 and 1.3 million cubic meters. In general, estimation recharge studies in Birjand aquifer indicate that the recharge value varies from 9 to 11 million cubic meters per year. These values are calculated baxsed on the water-table fluctuation and water-budget whose similarities verifies the results.