The behavior and mechanisms of the enantioselective degradation of beta-cypermethrin were studied in soil. The four isomers were degraded at different rates, and the enantiomer fractions of alpha-cypermethrin and theta-cypermethrin exceeded 0.5. Moreover, 3-phenoxybenzoic acid, phenol, and protocatechuic acid were detected; based on the presence of these metabolites, we predicted the degradation pathway and identified the functional genes that are related to this degradation process. We established quantitative relationships between the data on degradation kinetics and functional genes; we found that the quantitative relationships between different enantiomers differed even under the same conditions, and the genes pobA and pytH played key roles in limiting the degradation rate. Data obtained using path analysis revealed that the same gene had different direct and indirect effects on the degradation of different isomers. A mechanism was successfully proposed to explain the selective degradation of chiral compounds based on the perspective of functional genes.