Gas-liquid Chromatographic determination of trace 4-nitrochlorobenzene (PNCB) in the environment was inproved in this paper, and the problem of determining remainder of PNCB in plant and sediment was successfully sevolved. Aimed at providing scientific basis for prevention and control of PNCB pollution and data for the design and management of effluent esourcemental pre-treatment system, the fate of PNCB in the municipal wastwater pre-treatment system was emphatically studied. PNCB did not photo-degraded in water by natural light. One of the major paths of PNCB escaping from open water body was Votalizing through the gas-liquid intersurface. PNCB transformed and degraded insignificantly under erobic condition. It transformed and degraded to a certain extent under facultative condition, but was restricted significantly by the condition of dissolved oxygen(DO) in water. Therefore, it was not praticable to treat PNCB-efflent with aerobic stabilization pond, and not feasible with facultative stabilization pond. PNCB in low concentration was transformed completely under anaerobic condition the major middle metabolic product was PCA. Comparing to PNCB, the acute toxicity of PCA was slighter and the complete degradation of PCA by certain microorganisms under aerobic condition was easier. We suggested that transformation of PNCB to PCA effectively under anaerobic condition, and then degradation of PCA under aerobic conditon was a effective path of the elimination of PNCB in water.