The change of base resistance in Si-UJT under irradiation of 60Co γ-ray is provided. Through multipoint measurement and real-time monitoring, it was shown that the base resistance decreased immediately and then increased slowly. Compared with domestic and foreign related research results, this proves that the displacement effect is the main effect of base resistance in Si-UJT irradiated by 60Co γ-ray, but it lags behind the ionization effect from microanalysis of the interaction between γ-ray and Si material. This is very important for the radiation hardened research.