The concentration of chlorophyll-a is an important index of phytoplankton biomass that can reflect the status of ocean primary productivity. According to the analysis on the physicochemical environmental factors that affect the concentration of chlorophyll-a, we may clarify the dominant factors of ocean primary productivity. Two monitoring stations were situated on the sea area in Jiangmen, Guangdong Province, China. The survey was conducted from March to November 2010 to determine chlorophyll-a, water temperature, salinity, pH, dissolved oxygen (DO), chemical oxygen demand (COD), phosphate, nutrient N and oil in two stations. According to the principal component analysis (PCA), the application of the partial least squares (PLS) regression solved the multiple regression analysis including the multiple correlations between the environmental factors with a high precision; it also established the mathematical model with fewer monitoring data. In the PLS regression, the monitoring data were normalized, and then used the variable importance in projection and T² ellipse fitting-aided analysis technique for extraction. The regression equation of station A was y = 0.0076x₁-0.0806x₂-1.2869x₃+ 0.1498x₄-0.1905x₅ 126.6x₆ 5.985x₇-0.3538x₈ 10.84. The regression equation of station B was y= 0.0781x₁ 0.5852x₂ 0.4773x₃-0.5661x₄-38.11x₅ 0.8501x₆-4.429. The eutrophic index of station A was 0.041, suggesting that the water of Chuandao sea area was oligotrophic. The eutrophic index of station B was 1.005, suggesting that the water of Shadi sea area was eutrophic. The results showed that the main effective factors of chlorophyll-a were nutrients N and phosphate in oligotrophic waters of Chuandao sea area, and that COD, DO and water temperature were the effective factors of the ocean primary produ¬ctivity in Shadi sea area.