Abstract: Iron reduction particles, represented by zero-valent iron (ZVI), are widely used in the remediation of contaminated groundwater of chlorinated hydrocarbon. However, the reactivity towards refractory saturated chlorinated hydrocarbons and dominant influencing factors remain unexplored. Contaminated groundwater with high concentration of chlorinated ethane from an abandoned organic solvent plant in North China was collected, and the chemical reduction activities of four particle sizes (100 mesh, 200 mesh, 400 mesh, 800 mesh) of micro-scale zero-valent iron (mZVI), nano-scale zero-valent iron (nZVI) and pyrite on 1,1,2-trichloroethane (1,1,2-TCA) in the actual contaminated groundwater were comprehensively evaluated. The factors and laws affecting the reactivity of iron reduction particles were revealed by redundancy and correlation analysis. The results showed that the pseudofirst-order rate constant (k_obs) and mass normalized rate constants (k_M) of 1,1,2-TCA in nZVI reaction group were the highest, reaching 0.012 5 d⁻¹ and 0.008 L/(g·d), respectively, followed by mZVI, and the reduction of pyrite was the weakest. Although the increase of particle dosage could improve the degradation rate of 1,1,2-TCA, the reaction rate per unit mass decreased. However, contrary to traditional cognition, the specific surface area normalized rate constant (k_SA) was more dominant for mZVI, and the k_SA of 200 mesh mZVI was 22 times that of nZVI under the same additive quantity. Redundancy analysis showed that the content of impurities such as S, O, Cl, C and the dosage of particles restricted k_obs and k_M, while the content of O, C, S and specific surface area were most correlated with k_SA, and correlation analysis showed that O, C, specific surface area and k_SA were significantly negatively correlated. The results show that iron reduction particles with lower impurity content should be preferred in the design of the large-scale treatment of groundwater polluted by chlorinated hydrocarbons, and the appropriate amount of mZVI is more advantageous in terms of cost and surface utilization.