Six surveys were carried out to investigate the fishery resources and their habitat environments from May to October 2011 in the Laizhou Bay. Phytoplankton samples were collected using a standard vertical towing net (mesh size 77 μm), followed by the addition of formalin (approximately 5% final concentration in each sample) for preservation. Habitat environment was measured with a Multiparameter Sondes (YSI 6600). Phytoplankton species identification and cell enumeration were performed with an optical microscope. Phytoplankton community succession from spring to fall was clarified and its relationship with the density of major pelagic fishes was revealed by generalized additive models (GAM). A total of 33 genera and 78 taxa were recorded, with diatoms and dinoflagellates accounting for 85.9% and 14.1% in the total taxa numbers, respectively. Most of the species were eurythermal, and some were warm-temperate ecotypes, such as Rhizosolenia styliformis. Others were warm-water and oceanic species, such as . Two abundance peaks formed in the spring and fall seasons, with the values of 265×10⁴ and 111×10⁴ ind/m³, respectively. Monthly abundance from May to October was 265×10⁴, 53.1×10⁴, 27.1×10⁴, 27.7×10⁴, 111×10⁴, and 92.9×10⁴ ind/m³, respectively, with the diatoms accounting for 80.8%, 76%, 54.5%, 87.8%, 86.6%, and 68.7%. The monthly averaged ratios of dinoflagellate to diatoms abundance was 1.15, 1.13, 2.54, 0.23, 0.17, and 1.42, peaking in July. The dominant taxa were from late spring to early summer, from middle summer to middle fall. Monthly , 31.8×10³, 124×10³, 219×10³, 398×10³, and 188×10³ ind/m³, respectively, with the diatoms accounting for 32.7%, 18.7%, 34.8%, 51.7%, 49.3%, and 32.3%. , 8.57×10³, 19.9×10³, 22.4×10³, 250×10³, and 63.7×10³ ind/m³, respectively, accounting for 0.24%, 4.29%, 5.74%, 12.1%, 15.7%, and 13.3%. , 23.8×10³, 1.31×10³, 10.5×10³, 0.23×10³, and 1.24×10³ ind/m³, respectively, accounting for 4.14%, 9.64%, 5.49%, 15.9%, 0.045%, and 0.42%. 3, 0.57×10³, 3.76×10³, 68×10³, and 124×10³ ind/m³, respectively, accounting for 0.24%, 4.29%, 5.74%, 12.1%, 15.7%, and 13.3%. , 0.93×10³, 7.13×10³, 7.46×10³, 20.4×10³, and 33.7×10³ ind/m³, respectively, accounting for 0.032%, 0.39%, 3.36%, 5.42%, 2.8%, and 7.77%. The species richness, diversity and evenness increased markedly from late summer to middle fall. They had 72%, 70%, and 29.6% increases after August, respectively. The GAM analysis was fulfilled in the mgcv-1.8 package by R software. The stepwise optimized final model, as explained by environment and phytoplankton factors, clarified a sum of 76.5% deviance to the total CPUE (Catch Per Unit Effort) of four pelagic fishes (Engraulis japonicus). There were significant differences in the five predictor variables of month, sea surface temperature, abundance, and the ratio of dinoflagellate to diatom abundance, with stepwise deviation explanation of 52.3%, 8.6%, 9.3%, 0.5%, and 1.8%. It is clear that the long-term variations of the phytoplankton community structure and abundance level have made positive effects on the sustainability of the current status of fish communities and fishery resources in the Laizhou Bay. This study provides the baseline data and evidence from the view of phytoplankton diets, for further discussion of the factors that influence on the recruitment and food web processes of the fishery populations in the key habitats.