Small copepod Paracalanus parvus is the dominant zooplankton species for early larvae of fishes as food in the critical spawning and nursery habitat of Laizhou Bay, Bohai Sea. Annual dynamic distributions of the species in the bay were studied based on the zooplankton samples that were collected from May 2011 to April 2012 by a net with 50 cm diameter and 160 micron mesh size. In this study, stage-specific abundance of P. parvus from the original sorting was transformed before the multiple analysis including cluster analysis and multidimensional scale. Principal component analysis (PCA) and RELATE modules of BIOENV in software Primer 6.0 were used to seek the best matches of environmental factors that affect distribution of P. parvus. As the most common copepod in Laizhou Bay, P. parvus was observed at all stations during the investigated period. The species was more abundant from July to October compared with other seasons and its abundance peaked in August. By cluster analysis based on the copepod stage-specific abundance, three stations groups were recognized. The one was located on outside of Laizhou Bay near the central Bohai Sea; the second was located to the runoff inlet of the west of the bay; the third was appeared in the transition area of the two mentioned groups before. The abundance of P. parvus reached the highest in the transition group and the lowest in the group outside the runoff inlet. According to the results of BIOENV analysis, the surface water temperature and pH co-regulated seasonal distributions of P. parvus, while seawater salinity and depth had stronger effects on the spatial distributions. The significant correlations between seawater pH and Huanghe River runoff suggest that runoff one month earlier may be a possible indirect factor that affects the temporal variations of the P. parvus.