The diversity of aquatic macrophytes plays an important role in wastewater purification. To optimize poly-culture vegetation structure, Typha-Phragmites-Scirpus (with T. angustata, P. communis, S. validus as major species) vegetation, Typha-main (with T. angustata as major species) vegetation and Typha-monoculture vegetation as three design treatments were planted in pilot-scale gravel-based subsurface wetlands to treat artificial sewage. The Typha vegetation depicted had high COD, TN and TP removal loads in wetlands when low pollution load was treated, Typha-Phragmites-Scirpus vegetation had COD, TP and TN removal loads of 0.517 g m^-2 d^-1, 0.277 g P m^-2 d^-1 and 0.023 g N m^-2 d^-1 in autumn. A Partial Correlations Analysis showed that COD removal loads significantly and positively correlated with plant species and stem density in either pilot scale or medium-sized (430 m² in area) constructed wetland. The N, P amounts in the above-ground tissue are only 3.5~11.1 g N m^-2 yr^-1 and 1.3~13.5 g P m^-2 yr^-1 in medium-sized and pilot scale wetlands, because both biomass and N, P contents of wetland vegetation harvested in late autumn were low. Thus, it is important for constructed wetlands to optimize poly-culture vegetation structure to improve treatment efficiency. Generally, the poly-culture wetlands vegetation of T. angustata, P. communis, S. validus, Z. latifolia, Acorus calamus with stem densities of 23 stem m^-2, 194 stem m^-2, 112 stem m^-2, 26 stem m^-2, 42 stem m^-2 could gain excellent removal efficiency.