Abstract: To study the degradation effect of floating bed cultivation of Polygonum cuspidatum on differentconcentration ammonium salt, the floating bed cultivation of Polygonum cuspidatum was constructed in big indoor bucket, the water quality indexes (TN, NH4+-N, NO3--N, NO2--N, TP) were tested by adding different concentrations ammonium salt. The results showed that the TN concentrations of four different concentrations of ammonium salt decreased from the 5th to the 13th day, and increased on the 17th d. The concentration of NH4+- N in the 10 mg/L ammonium salt group decreased from the 5th to the 13th day. The NO3--N concentration from the open water area group with 5 and 10 mg/L ammonium salt initially increased and then decreased, and those from the root zone reached the peak on the 5th and 9th day, respectively. The NO2--N concentration in the 10 mg/L ammonium salt group increased to the peak on the 5th day, while it dropped to 0 on the 13th day. The TP concentration in the control group was higher than those of the other groups. The concentration of TN, NH4+-N, NO3--N and NO2--N can be degraded by floating bed cultivation of P. cuspidatum from the 5th to the 13th day, while the concentration of TP dropping to 0 needs more time.