Abstract: Based on the zooplankton samples that were collected from the coastal waters of Hainan Island in the early summer of 2011,the factors such as species composition,dominant species,abundance,ecological groups,Shannon-Wiener index and evenness of zooplankton were analyzed,and the relationship between zooplankton and environmental factors was discussed in this paper. The result showed that 164 species of holozooplankton and 11 groups of nlerozooplankton were identified,among which Copepods were the most diverse with 82 species in 40 genera. The dominant species were Echinodermata larva,Penilia avirostris,Oikopleura dioica,Macrura larva,Flaccisagitta enflata,Oithona plumifera,Doliolum denticulatum,Lucifer intermedius,Globigerina bulloides and Acrocalanus gracilis. The average zooplankton abundance in the coastal waters of Hainan island was 1 348.68 ind/m³,with the highest abundance in eastern waters. Zooplankton abundance in eastern coast showed the trend which decreased from near to far,while the abundance in Beibu gulf and southern coast showed the trend which increased firstly and then decreased from near to far. Influenced by the coastal current and South China Sea warm current in the early summer,the most of zooplankton ecological groups were warm water coastal group and eurytopic group in the coastal waters of Hainan Island. The average Shannon-Wiener index and evenness of zooplankton were 3.03 and 0.72 respectively. The Shannon-Wiener index and evenness were lower in eastern coast result from the explosive growth of nlerozooplankton. Correlation analysis revealed that zooplankton abundance had obvious negative correlation with pH (p<0.05,r=-0.360),and obvious positive correlation with phytoplankton abundance (p<0.01,r=0.395). Furthermore,zooplankton abundance showed a distinct correlationship with the other environmental factors,of which salinity,DO,COD_Mn,NO₃-N,NH₄-N and PO₄-P were positive,while water temperature,NO₂-N and SiO₃-Si were negative in the coastal waters of Hainan island.