Canna generalis was often used to purify polluted river by floating bed, while the floating bed of Festuca arudinaces was less used. The purification of seriously polluted river in winter by Festuca arudinaces of different floating-bed coverage rates was carried out to find the best coverage rates in heavy polluted river, Suzhou City. The results showed that Festuca arudinaces had a high ability to remove nitrogen, phosphorus and COD in eutrophicated water, and the water clarity (SD) was raised effectively. Future engineering for improving water quality of heavy polluted river in winter would be favorable through the use of floating bed of Festuca arudinaces.