Abstract: Activation energy of hydroxyl radical OH reacting with alkanes was estimated from the quantitative relation between the bond dissociation energy (BDE) of Ri-H and the polarizability effect index (PEI) of alkyl radical Ri. Preexponential factor A in Arrhenius expression quantitatively was related to the topological steric effect index (TSEI) of alkyl radical Ri. The research results show that three parameters, PEI, TSEI and temperature T, can be used to quantify the activity of hydroxyl radical reacting with primary, secondary and tertiary carbonhydrogen bonds in alkane. The expression can accuratly evaluate the activity of C-H bonds. Moreover, the PEI and TSEI of alkyl radical Ri can be correlated quantitatively with the reaction absolute and relative rates of alkanes and cyclanes with hydroxyl radicals at various temperatures. The predicted rate constants are in good agreement with the experimental ones.