Based on the principal component analysis (PCA), data from 25 marine monitoring stations in Tangshan Bay from 1995 to 2012 were collected to study the change of nutrient composition in Tangshan Bay under anthropogenic influence. Results showed that the inorganic nitrogen (DIN) presented an obvious  increase trend in the near 20 years, while the PO₄^3--P and SiO₃^2--Si presented a decrease trend. The average N：P ratio increased from 3.0 in 1995 to 26.0 in 2012, but the average Si：N ratio decreased, indicating the nutrient structure in seawater had substantially changed in the near 20 years. According to the results of PCA, the change of water quality was identified. The analysis extracted the first two principal components (PC). PC1 was associated with DIN, NO₃^--N, NH₄⁺-N, PO₄^3--P and NO₂^--N, which explained 71.5% of the variance. PC2 was characterized by Chl a and SiO₃^2--Si, which explained 21.8% of the variance. It indicated that the water quality of Tangshan bay was closely related to DIN and PO₄^3--P. The two principal component scores revealed the interannual change trend of water quality in the Tangshan Bay under anthropogenic influence, which changed from the N limitation before development and at early stage of development (1995-2005) to the P limitation after development (since 2007). The nutrient composition in Tangshan Bay had changed significantly under anthropogenic influence, therefore, special attention is needed on the the change of nutrients in seawater of Tangshan Bay, especially the increase of inorganic nitrogen content.