Abstract: Based on the data of macrobenthos collected from the surveys of 4 cruises which were conducted in Mar., May, Sep., Dec. 2004 in Daya Bay, South China Sea, the species diversity of macrobenthos was studied. The results showed that nowadays the level of species diversity was lower than that in 1987 due to the more impacts of human activities on the bay since then. In 2004, the number of macrobenthos species was 79. The mean of richness index(I), evenness index(D) and Shannon-Wiener index(H') were 1.17, 0.74 and 2.06, respectively. The seasonal changes of each diversity index was small, without significant different (P0.05). The level of species diversity showed the trend of winter spring summer autumn. It has been found that the distinct change of dry and wet season, the species diversity in wet season was higher than those in dry season. The species diversity of macrobenthos in outer Bay was the highest among other areas. The dominant species of Veremolpa micra and Timoclea scabra were so abundant that the species diversity of macrobenthos in center Bay and inner Bay were low. The seasonal change of the species diversity of macrobenthos in center Bay and inner Bay was caused by the change of the abundance of V.micra and T.scabra. Then the abundance of V.micra and T.scabra fluctuated with the water temperature directly.