Abstract: The characters and influencing factors of the degredation of organophosphorus pesticides of methamidophos, chlorpyrifos and monocrotophos by hydrogen peroxide (H_2O_2) were studied. The result showed that hydrogen peroxide had highly activity in degrading the organophosphorus pesticides, and the degradation rates were 5-13 times of that of the treatment without H_2O_2.Ultraviolet radiation could significantly increase the degradation of the pesticides, which were 3-9 times of the treatment with daylight, and 10-20 times of the treatment without light. When the initial pH-value was at 4-6,the lest degradation rates were gotten, while the rates increased with high basic condition. However, the degradation was restrained with the use of O_2. The degradation rates increased with the time of reaction. The degradation of pesticides was expected to get even better results at higher concentration of H_2O_2 concentration, and the degradation rates was decreased with more chemical added, however, the degraded amount increased.