Polarized excitation emission matrix(PEEM), combining advantages from both polarized technology and excitation emission matrix (EEM), is a analytical tool with higher selection, accuracy and sensitivity, which could provide complete information for molecular characterization. The degradation of benz［a］pyrene by potassium ferrate was further studied by PEEM in this paper, and the degradation features were also deeply discussed through polarized values and PEEM changing. According to the experiment, for t=15 s, the degradation rate was 60%; while for t=40 s, above 90%. Polarized value characterized more clearly the difficult degradation of benz［a］pyrene. The first order kinetic equation also obtained: y=0.277x－0.004(r=－93.90%), by fitting the time polarized curve. These results are accord with the psevious results obtained from EEM’s characterization, which provide a very useful conference for method selectivity in researching process and mechanism of pollutants’ degradation.