Abstract: N-nitrosamines (NAs) are a class of disinfection by-products with high toxicity and strong carcinogenicity. These compounds can be generated from the reaction of their precursors with disinfectants. They were widely occurred in the water environment. The generation of NAs pollutants can be suppressed by the control of their precursors. This study took the waters of the Xijiang, Beijiang and Dongjiang rivers in the main streams of the Pearl River. We explored the distributions of NAs precursors in the river water. GC-MS/MS was used to detect the concentrations of NAs FP (formation potential of NAs) produced by chloramination. The sources of NAs precursors were analyzed based on the principal component-multiple linear regression analysis (PCA-MLRA) method. The results showed that six NAs were observed after chloramination, including NDMA FP (formation potential of NDMA), NMEA FP (formation potential of NMEA), NDEA FP (formation potential of NDEA), NPYR FP (formation potential of NPYR), NMOR FP (formation potential of NMOR) and NDBA FP (formation potential of NDBA), while the average contents were 19.4, 33.3, 3.2, 5.3, 2.6 and 3.0 ng/L, and their detection rates were 100%, 3%, 90%, 84%, 53% and 84%, respectively. After chloramination, the concentrations and detection frequencies of NDMA FP, NDEA FP, NPYR FP and NMOR FP increased significantly compared with the original water samples, especially for NDMA FP and NPYR FP, and the spatial distribution trend was followed the order Beijiang > Xijiang > Dongjiang. According to the results calculated from PCA-MLRA, 91% of the NAs and their precursors in the main stream of the Pearl River came from industrial wastewater and aquaculture wastewater pollution, while only 9% were caused by agricultural activities and domestic sewage discharge. The research showed that the precursors of NDMA and NPYR were the dominant compounds in this area. Industrial wastewater and aquaculture wastewater were the main sources of NAs and their precursors in the main stream of the Pearl River.