The accurate estimation of fracture geometry parameters and the characterization of rock mass structure are two important topics in the geological disposal system of high-level radioactive waste (HLW). The Beishan area, as the current preselected area for China's HLW disposal, has three subareas considered to be the key survey area at the stage of site selection. In this paper, a comprehensive survey method conducted on the outcrop is developed to estimate fracture geometry parameters. Results show that fracture occurrence obeys a Fisher distribution, fracture trace length obeys a normal distribution, and the distribution of spacing obeys a negative exponential distribution. An evaluation index, Rock Mass Structure Rating (RMSR), is proposed to characterize rock mass structure for the three subareas. The results show that the Xinchang area is more suitable to act as China’s HLW disposal repository site. At the same time, the index can also be applied to characterize surface rock mass structure and rock mass integrity at the site selection phase of HLW disposal.