Abstract：Through analyzing the geological structure，hydrogeology，geophysics and borehole data in Jiujing block，a simple 3D geological model was constructed by using the correspondence software for Jiujing block，Beishan area，Gansu Province. On the basis of the 3D faults stable fluid field，the 2D matrix diffusion and sorption，the nuclides decay were calculated and simulated by using RockFlow. Simultaneously，the underground fluid and nuclides migration in the matrix and fault were simulated，and the temporal and spatial distributions of underground fluid and nuclides were also studied. The result shows that the 3D geological model is a very useful site assessment method，from which the spatial distribution of the host rock and faults can be displayed directly. Secondly，the key migration channel of nuclides is fracture；and the nuclides migration speed is affected by the porosity，permeability and diffusion coefficient of the matrix. The larger of these parameters are，the faster of the nuclides migration speed is. The nuclides migration is retarded by the matrix sorption，but the decaying coefficient has a limited influence on the nuclides migration. Thirdly，combining with 3D geological model and RockFlow，the fluid and nuclides migration are simulated；and the modeling results can provide references to the engineering design and safety assessment.
