Abstract: To determine the electromagnetic compatibility characteristics of the Five-hundred-meter Aperture Spherical radio Telescope (FAST) and its surrounding Public Mobile Telecommunications (PMT) system, this paper comprehensively discusses the electromagnetic interference caused by the PMT base stations of China Mobile, China Unicom, and China Telecom, the three major operators in the FAST radio quiet zone. Firstly, this paper starts with the spectrum division of the radio astronomy service, discusses the types of interference sources in the radio astronomy service, and introduces its operation protection standards. Then it details the frequency regulations and protection requirements of its radio quiet zone for the FAST. Secondly, it analyzes the ITU-R recommended radio wave propagation prediction and interference analysis method, and the applicability of the method is verified through field measurements. Furthermore, it analyzes the electromagnetic radiation propagation characteristics of PMT base stations and comprehensively evaluates the interference caused by PMT base stations in the FAST radio quiet zone. The results show that 90.24% of the PMT base stations will interfere with the FAST to some extent. And under the selected analysis conditions, only 43.14% of the data met the FAST protection requirements. Finally, to suppress and eliminate interference signals from PMT base stations, we analyze commonly used radio frequency interference suppression methods in radio astronomy. At the same time, to protect the FAST from interference from PMT base stations, we discuss feasible frequency protection measures from the perspectives of the FAST and PMT base stations, and establish an evaluation system for protection methods from four categories of indicators, including implementation difficulty, economic cost, strategic benefits and communication quality, and provide examples to illustrate the proposed protection methods. The above research results can provide a technical basis for ensuring the safe observation of the FAST.