The invention discloses a tunnel initial support stability judging and prediction method based on an electromagnetic radiation. The tunnel initial support stability judging and prediction method includes the following steps that: S1, as for dangerous section (includes not-to-be-ring section and be-ring section of the initial support) possible to be instable failure of the initial support, monitoring sections are circularly arranged at certain intervals, and electromagnetic radiation monitoring sites are arranged at representative positions of the monitoring sections; and S2, portable electromagnetic radiation monitor is adopted to monitor the intensity of the electromagnetic radiation on the surface of the tunnel initial support of each monitoring site at different period, and normal tunnel deformation monitoring is simultaneously conducted at each monitoring site. According to the tunnel initial support stability judging and prediction method, any equipment does not need to be pre-buried, test in the field is convenient, construction is basically not interfered, testing in a wider range can be conducted, and the method is suitable for being widely adopted in a tunnel project undercomplex geological conditions; and the monitoring results can reflect the relative small and large and changing trend of surrounding rock pressures, and key part of initial support transformation anddeformation, and the basic need of stability analyzing and estimating of the initial support can be met.