Abstract: Some predictions were made for Tangshan strong after shocks and modearately strong earthquakes in the junction area of the northern three provinces by Beidaihe seismic situation window, some earthquake examples for practical usage and the prediction indexes for magnitude and time were obtained. It is suggested that we should search for a certain number of "seismic situation windows" around the Tanhsgan seismic region to form a regional window network to predict Tangshan late strong after shocks or to monitor and predict moderately strong earthquakes occurred in new regions.