Abstract: Effects of heavy metals on soil denitrification rates in wetland ecosystems has attracted much attentions with accelerated global warming and anthropogenic activities, but few studies have evaluated the low-dose effects under various plant types. In the present study, soils were collected from bare beach, Spartina alterniflora and Phragmites australis in Chongming Dongtan wetland, Shanghai, China. Gradient doses of Cd (0, 0.05, 0.1, 0.3, 0.5, 1.0, 3.0 and 5.0 mg·kg^-1) were added into the soils, and the Den rates were determined based on 15N isotope tracer technology. The results showed that mean Den rate in soils with Phragmites australis (9.2±0.3 μg·kg^-1·h^-1) was higher than that of Spartina alterniflora (4.7±0.5 μg·kg^-1·h^-1). The presence of Cd resulted in the significant decrease of Den rates under the two vegetation (P<0.05). The soil Den rates under Phragmites australis and Spartina alterniflora decreased to 6.3 μg·kg^-1·h^-1 and 3.2 μg·kg^-1·h^-1, respectively. Under Cd stress, the change of Den rate showed a "step-like" mode with doses. In the low dose (0.05-0.3 mg·kg^-1) interval, the inhibition rate of Den rates remained stable at 13.3%-14.8%. When the dose of Cd increased to 0.3-0.5 mg·kg^-1, the inhibition rate increased from 14.8% to 50.0%. At high doses (0.5-5.0 mg·kg^-1), the inhibition rate reached a higher level and stabilized again (50.0%-55.0%). Correlation analysis showed that the soil NO3^--N contents were significantly positively correlated with Den rates under Spartina alterniflora and Phragmites australis (P<0.05). This indicated that the presence of low-dose Cd did not change the dominance of NO3^--N on the Den process in the coastal wetland.