Abstract: By comparative analysis of the relatively strong after shocks(M_L ≥4.9 after 1978)after the Tangshan M7.8earthquake in 1976 and the moderately strong earthquakes in North China area,it is found that the relatively strong after shocks in Tangshan show a correlatability with the moderately strong earthquakes in North China area,and the corresponding probability has been given which has provided a quantitative basis for the prediction of notable earthquakes occurred in Tangshan in the future.