The three-component model is often used to invert the phytoplankton size class (PSC) concentration globally, especially in open oceans. Limited by the three-component model’s assumption, new efforts were made to explore PSC in different water environments. Mass global cruise data sets were gathered and classified into coastal, mixed, and open ocean data sets depending on the variation in bathymetric depth. A new power three-component model was established for coastal water samples (<50 m), where the determination coefficient (R2) were 0.99, 0.51, and 0.38 for micro- (Micro), nano- (Nano), and picophytoplankton (Pico), respectively. We also updated the coefficients of the exponential three-component model in open ocean (>200 m) and found that the PSC verification results performed better in the north of −40°N oceans (R2: 0.83, 0.70, and 0.64, respectively). A smooth function for the samples in mixed ocean waters (50–200 m) was designed to obtain PSC by different weights between the power and exponential three-component models with relatively low accuracy (R2: 0.84, 0.37, and 0.14, respectively), indicative of the complex conditions in these regions. We assessed the published models’ performance in coastal and open ocean samples and found an apparent underestimation of the Nano and Pico chlorophyll concentrations when their concentrations were larger than 0.2 mg m-3. The PSC proportion distribution was consistent with existing knowledge. This study evaluated the preliminary consideration of the assumption of the exponential three-component model and found that it may fail in the South Ocean, based on the global open ocean data set.