The working principle of the optic fiber SPR sensor was discussed in the present paper at first. The feasibility of using it to monitor the degradation process of the environmental sewage represented by the methyl orange was studied. Finally, the optic fiber SPR sensor was adopted to monitor the change in degradation concentration represented by the original methyl orange solution on the base of 50 mL initial concentration 30 mg x L(-1), and the optic fiber SPR spectrum character of degradation process was analyzed in detail. Meanwhile the UV spectrophotometer was used to measure the change in concentration in the course of the degradation. The measurement data were analyzed and compared at large. The research work indicates that both the methods have consistent results, as the degradation time increases, the absorbance and concentration of the environmental sewage represented by the methyl orange solution decrease by and by, and the resonant wavelength of the optic fiber SPR sensor blue shifts step by step, as compared to the original standardization methyl orange solution resonant spectrum. It was shown that the methyl orange solution was degraded, and the rate of degradation was up to about 73 percent within two hours. The comparative results illustrate that it is feasible to use the optic fiber SPR sensor to monitor the environmental sewage degradation. The research result not only provides a new monitoring method for the degradation process of the environmental sewage, but also promotes the technique of the SPR sensor combined to the environment monitor by a long way.