Jingdong 120m large aperture fully movable radio telescope under planning and construction is the largest aperture telescope under construction or built in the world, which will be equipped with 1-7GHz broadband feed and receiver. In order to make the best of the telescope, it is necessary to analyze and study its electromagnetic compatibility characteristics. So the following contents should be determined, first, the influence of interference sources on radio telescope must be evaluated; second, the interference protection limit of radio telescope must be calculated; third, the interference power of interference sources reaching feed port must be determined; fourth, the propagation loss of electromagnetic wave with distance must be considered; fifth, the gain of antenna to interference signals must be determined according to position relationship between interference source and antenna. Through the above process, electromagnetic shielding indexes required by each interference source be obtained. As a result, it lays a foundation for EMC design of telescope in the detailed design stage and implementation in construction process, and provided a strong guarantee for improving comprehensive performance, scientific research outputs and observation efficiency of l20m radio telescope.