A wastewater culture system was designed to study root growth of eight species of wetland plants. The system included a plastic barrel (top diameter = 36.5cm, bottom diameter = 30.0cm，height = 34.5cm) for holding wastewater and a foam plate for holding the plant. Four species, i.e., Canna indica Linn., Cyperus alternifolius subsp. flabelliformis (Rottb.) Kukenth, Pennisetum purpureum Schum. and Vetiveria zizanioides (Linn.) Nash, with fibril root system and another four species, i.e., Acorus calamus Linn., Hymenocallis littoralis (Jack.) Salisb., Phragmites communis Trin., and Typha angustifolia Linn. with rhizomatic root system were comparatively studied. Results indicated that root growth of the plants with fibril root system was faster than that of the plants with rhizomatic root system. After ten weeks’ cultivation, average root number of fibril root species reached 1349 per plant while average root number of the plants with rhizomatic root system only reached 549 per plant. Our study also showed that average root biomass of fibril root plants was 11.3g per plant while the average biomass of rhizomatic root plants was 7.4g per plant. Fine root biomass of diameter <1mm made up 51.9% of total root biomass in fibril root plants, while it comprised only 25.1% in rhizomatic root plants. The ratio of root biomass to shoot biomass of rhizomatic root plants was 0.2, which was higher than that of fibril root plants (0.1). Root surface area of the fibril root plants (6933 cm² per plant) was considerably larger than that of rhizomatic root species (1897cm² per plant). Rhizomatic root species showed longer root lifespan (46.6 days) than fibril root plants (34.8 days). C. indica had more developed root system than other plants, with root number 1871 and root surface area 22832 cm² per plant.