Abstract: In this paper， acute toxic experiment of petroleum hydrocarbon water - accommodated fractions was done on Chlamys nobilis. The results showed that acute toxic data of 24h LC50，48h LC50，72h LC50and 96 h LC50were 233.08，147.30，81.67 and 75.16 mg/L respectively，and the safe concentration was 17. 65 m g/L. Accumulation effects of different concentrations of petroleum hydrocarbon water - accommodated fractions were also done on Chlamys nobilis. The results showed that accumulation effects were proportional to concentrationand time in 120 hours. In stress of different concentrations of petroleum hydrocarbon water – accommodated fractions，the activitiy of POD and SOD in Chlamys nobilis showed characteristics of promoting by low concentration and inhibiting by high concentration，and the activitiy of AKP in liver and gills in Chlamys nobilis could be promoted.