In this research, an experimental laboratory plant was constructed in order to evaluate the effect of organic, nitrogenous and phosphorus loads on the removal efficiency and behavior of duckweed based wastewater stabilization ponds. The results of the study showed that; covering the oxidation ponds with duckweed improve their ability to treat higher organic and nitrogenous loads. In addition, covering the oxidation ponds with duckweed improve their ability to treat higher organic and nitrogenous loads. Organic and nitrogen load can be increased from (65 kg/ ha. day) to (158 kg/ ha. day) and from (49 kg. ha. day) to (111 kg/ ha. day) by covering the ponds by duckweed. On the other hand, the results of research also showedthat; increasing nitrogen and phosphor load leads to decrease removal efficiency of nitrate, nitrite, and increases removal efficiency of ammonia and phosphate at the same hydraulic retention time.