Abstract: The biodegradation kinetic constants K of eight kinds of alkyl phenols by Tolypothrix were obtained by simulating the degradation process with the second-order kinetic equation. Many physicochemical parameters of eight alkyl phenols were calculated using PM3 method contained in the semi-empirical molecular orbital package (MOPAC) and referring to other literatures. With regression analysis by the computer software SPSS, the quantitative structure-biodegradability relationship (QSBR) study was made for biodegradation data lg K. The results indicate that lg K_OW, M_w,¹X^ν ,²X^ν,ΔH_f and μ can well correlate with the rate of alkyl phenols biodegradation, in which ²X^ν has the best simulating effect. On this basis, preliminary analysis of alkyl phenols biodegradation mechanism holds that steric parameters were dominant factors governing the biodegradability of alkyl phenols; but the effect of ΔH_f and electronic parameter μ on the final biodegradation products should not be ignored.