In this paper, a groundwater hydrological study of the Gyeongju well during the Silla period is conducted to investigate how sufficiently the Gyeongju well supplied water demand at the time. It is assumed that the current geology and soil condition in Gyeongju remain similar to the Silla period. Also, the land use and land coverage during the Silla period is estimated based on the current land condition in Gyeongju. Precipitation during the Silla period is analyzed using precipitation data from 1984 to 2014 provided by Gyeonju weather station. Precipitation analysis is applied based on 3 different scenarios; precipitation intensity during the Silla period was Case ① the same as, Case ② 30% more, and Case ③ 30% less than the precipitation intensity of the last decade (2005~2014). Furthermore, to observe the use of the well in Gyeongju during droughts, the following condition(Case ④) is also considered; ten year drought during the Silla period was the same as the ten year drought from 1984 to 2014. Available amount of groundwater development is analyzed using NRCS-CN method. The results show that the potential amount of groundwater in Gyeongju during Silla era was for Case ① 62,825,272 ㎥/year, Case ② 93,606,567 ㎥/year, Case ③ 32,277,298 ㎥/year, and Case ④32,870,896 ㎥/year. Also, it has been shown that 45,260,000 ㎥ of groundwater were required to supply to all households in Gyeongju during Silla era. Therefore, if the precipitation intensity during Silla era was similar with the last decade, the groundwater would provide enough supply to all households in Gyeongju. However, in the case that the precipitation intensity during Silla era was 30% less than the last decade or a ten year drought happened, it is predicted that the water use in Gyeongju would have been limited.