A Pseudomonas strain P3 was isolated in this work. P3 can grow with p-nitrophenol as the sole carbon and nitrogen source. Growth in media with nitrogen, P3 can degrade p-nitrophenol to accumulate nitrite in the culture media. P3 can utilize a series of aromatic compounds as sole carbon sources. Different heavy metal ions have different effects on the degradation of p-Nitrophenol by P3. Glucose had no effect on the degradation of p-nitrophenol, while trace yeast extract greatly increased the degradation rate. Methyl parathion hydrolase gene mpd was clone into P3 by conjugation and genetically engineered bacterium PM was obtained. Methyl parathion hydrolase was expressed by PM. PM could grew on methyl parathion as sole carbon source. PM could degrade methyl parathion with relatively high activity and stability.