Abstract: Based on the data collected from six stations of Daya Bay in March 2004, the species composition and spatial distribution of heterotrophic bacteria in surface water of Daya Bay were determined. The results showed that the range of heterotrophic bacteria quantity was7.15102~91.0102 cfumL-1. The number of heterotrophic bacteria gradually decreased from bayhead to baymouth in Daya Bay. The 19 heterotrophic bacteria were identified by Biolog microbes identification system. They were gram-negative bacteria, belonging to 14 species 10 genera. Aeromonas sp., Vibrio sp. and Burkholderia sp. were dominant genus, and A.schubertii (DNA group 12), V.mimicus and B.glumae were dominant species in surface water in Daya Bay.