Abstract: High temperature reactor-modular pebble bed (HTR-PM) graphite core structure is recognized as multi-body structure that introduced complicated non-linear issues into the investigation of dynamic characters. Many attempts were made to research this issue, however, problems still remained. In this paper, a numerical analysis model was introduced, which simplified graphite/carbon bricks as mass point with rotary inertia and contacts of the components as connectors. The parameters of the connectors were obtained from relevant tests. Numerical analysis results match the tests displacement results of 1∶1 four-brick-two-layer graphite assembly. Moreover, the numerical model is insensitive to parameters. Hence, this model can be applied in HTR-PM graphite core structure dynamic response under seismic loads with precision and lower calculation cost.