Abstract: Dechlorination of crude oil is an effective way to alleviate corrosion in refinery units, and the critical process is the removal of organochlorine which can be efficiently removed through nucleophilic substitution reaction catalyzed by phase transfer. Herein, seven typical chlorinated alkanes were selected as model compounds to study the mechanism of dechlorination of crude oil by phase transfer catalyst in the nucleophilic substitution method, and a new dechlorination reagent using hexamethyl quaternary ammonium hydroxide with two quaternary ammonium groups as phase transfer catalyst, ethylenediamine as nucleophile and ethanol as solvent was developed. The results show that the dechlorinating performances of the dechlorination reagent on the model compounds are as follows: epichlorohydrin > 1,2-dichlorobutane > 1,2-dichloroethane > 1,3-dichloropropane > 2-chloropropane > 1-chlorobutane > chloroisobutane, and the results of the reaction kinetics show that epichlorohydrin with epoxy structure has the lowest activation energy in the process of nucleophilic substitution reaction by the phase transfer catalyst which makes it easier to be removed by the dechlorination reagent. The removal rate of epichlorohydrin can reach up to 99.4%. The optimal dechlorination reagent used ethylenediamine as nucleophile, ethanol as solvent and hexamethyl quaternary ammonium hydroxide as phase transfer catalyst. The dechlorinating rate of the Iranian crude oil reached 71.6 % at the reaction temperature of 95°C, the reaction time of 90 minutes, the dechlorination reagent dosage of 1000 mg/kg and the 6:1 molar ratio of phase transfer reagent and nucleophile. In addition, the mechanism of phase transfer in nucleophilic substitution reaction of chloroalkanes is investigated in the paper.