We studied the two characteristics of the 1V active episodes in seismic belt of Southeast China coast in 20th century. The one is the corresponding relation between the southeast coastal seismic belt and the Yangjiang seis- mic window, the other one is the seismic precursory significance about ME4 earthquakes which wasn't occurred for a long time. The results showed that the active of ME3 earthquakes in Yangjiang were affected not only by M5 earthquakes occurred in Yangjiang, but also by M 〉 5 moderate-strong earthquakes occurred in seismic belt of Southeast China coast in 1V active episodes. Before the moderate-strong earthquakes, occurrence frequency of ML3 earthquakes in the slip with every 3 months in Yangjiang raised, so ML3 earthquakes in Yangjing can be as the seismic window in seismic belt of Southeast China coast. In active episodes of seismic belt of Southeast China coast, the occurrence time interval ATe〉300 d of ML4 earthquake was the index of M5 earthquake in short-term or medium-short term prediction. However, ML4 earthquakes weren't occurred for a long time, which were normal appearances of the regional stress field in relaxed state. However it wasn't the seismic precursory signifi- cance in quiet episodes.