The clean and biological effect of Pistia stratiotes under different concentrations of livestock wastewater is first studied in indoor simulated conditions，which is collected from nature wetland. The correlation between clean and biological effect is also studied. The results show that the highest removal rates of CODcr，ammonia nitrogen，total phosphorus reach 82.33%，69.21% and 45.88% respectively. After 8 days of livestock wastewater stress，the enzyme activity of antioxidant system of Pistia stratiotes shows overall downtrend. The main protect enzyme in Pistia stratiotes is POD，whose variation range is the most obvious，and its sensitivity and irritability is the strongest. The correlation between removal effect and biological effect is substantially strong.