The different carbendazim concentration treatments including 300 (high), 600 (medium) and 1 200 (low) diluent of 50% wet carbendazim powder were applied on the soil where Spartina anglica grew in the field experimental plots. The morphological plasticity, clonal characteristics and biomass allocation patterns of S. anglica under the treatments were examined. There was no significant effect on culm height, number of leaves, leaf thickness, leaf area and root length (p>0.05) with 3 carbendazim treatments. Meanwhile, the node number of rhizomes and branching intensity of the species under medium concentration treatment were significantly higher than those of CK and the other treatments (p<005). However, total rhizome length and spacer length were significantly higher than those of CK and low concentration treatment and are not significantly different from those of high concentration treatment. More biomass was allocated to under-ground organs and less biomass to above ground parts with high concentration treatment (p<0.05). Consequently, the results implied that medium concentration of carbendazim treatment enhanced the clonal growth and the population sustaining and regenerating ability of S. anglica. We might draw the conclusion that the decline of S. anglica in coastal China resulted from infection of some fungus in the natural sediment.