In order to solve the time-consuming and labor-consuming problem in the traditional radio telescope site surveying task, Global Navigation Satellite System (GNSS) surveying technology is introduced to realize an unattended reference point (RP) monitoring method at a radio telescope. We design the algorithm of the reduction of the GNSS observations, including data matching, data verification, subsequent precision evaluation and so on. The GNSS target positions and other real-surveyed data of Sheshan 25-m VLBI (Very Long Baseline Interferometry) radio telescope collected in 2018 are used to perform data preprocessing, solution and RP determination and so on, which proves the feasibility of the method. The result shows the formal precision of the determined RP can reach up to 3 mm based on the subset of the observations (5%, $ $7600 GNSS tracking points) in a single day. In addition, some experiences and lessons in the pilot test of the unattended surveying at a VLBI station are summarized, and the problems that should be paid attention to in the process of using this method are clarified, which provides an important reference for high-precision site surveying in the future.