The mechanism of deactivation of Cu/Zn catalyst poisoned by organic chlorides in hydrogenation of methyl laurate to lauryl alcohol in a slurry phase was studied in a stirred autoclave. The catalyst was prepared by co-precipitation, and the un-poisoned and poisoned catalysts were characterized using XRD, BET, ICP-AES and SEM, respectively. The results indicated that both of catalytic activity and selectivity decreased with increasing amount of chlorides in methyl laurate. According to the characterization of the catalysts, the main causes for the chlorine deactivation of the Cu/Zn catalyst were that the chlorides could modify the valence state of active sites, decrease the BET surface area, and promote the growth of crystal and catalyst agglomeration. Further investigation indicated that chlorine atom decomposed from the chlorides combined with ZnO to produce ZnCl2, which could be dissolved in the liquid and promote ester-exchange reaction to lauryl laurate as Lewis acid.