Abstract: A fraction of the Kuroshio flowing east off the Philippine coast intrudes into the northeastern South China Sea (NESCS) through the Luzon Strait. The intrusion which takes place in winter can improve primary productivity in the oligotrophic NESCS greatly. Thus, study of the effect of Kuroshio intrusion on primary productivity will provide important references for predicting fish productivity and fishing operations. The data from satellite observation from 1997 to 2014 show that winter intrusion of the Kuroshio has enhanced primary productivity in the open waters remarkably and the area influenced could cover as large as one half of the oligotrophic northern SCS. Since 1997, without exception, the primary productivity in the NESCS has exhibited the lowest values in summer but the highest ones in winter. Impacted by a strong El Niǹo event, the primary productivity was exceptionally low in 1997 and 1998, and since 1999 the winter and annual primary productivities in the NESCS have shown a significant decreasing trend. Based on the spatial and temporal patterns of primary productivity and sea surface current, the analysis also determines the major types of Kuroshio intrusion path for every winter. The results show that for the 17 winters since 1997, the looping path, leaking path and leaping path of Kuroshio intrusions have all occurred and the winter intrusion mostly taken the path of a SCS branch. However, statistical tests show no significant difference of primary productivity in the NESCS between the Kuroshio intruding paths in winter.