A method for preparing 1,2-dichlorohexafluorocyclopentene, comprising: in step one: pyrolysing dicyclopentadiene, as raw material, to obtain cyclopentadiene, with nitrogen or other inert gas as a diluent in a molar ratio of the diluent to dicyclopentadiene of 1: 0.5 to 3, wherein the pyrolysing is at a reaction pressure of 0.1 MPa to 1.5 MPa, a reaction temperature of 300 °C to 450 °C and a contact time of 5 s to 30 s; in step two: subjecting cyclopentadiene, as raw material, to a chlorination reaction in a liquid phase with chlorine to obtain 1,2,3,4-tetrachlorocyclopentane, in a molar ratio of chlorine to cyclopentadiene of 1 to 3: 1, wherein the chlorination reaction is at a reaction temperature of 0 °C to 40 °C, and a reaction time of 1 h to 10 h; in step three: subjecting 1,2,3,4-tetrachlorocyclopentane, as raw material, to a chlorofluorination reaction with hydrogen fluoride and chlorine in a gas phase in the presence of a chromium-based catalyst to obtain 1,2-dichlorohexafluorocyclopentene, in a molar ratio of 1,2,3,4-tetrachlorocyclopentane, hydrogen fluoride and chlorine of 1: 5 to 20: 5, wherein the chlorofluorination reaction is at a reaction pressure of 0.1 MPa to 1.5 MPa, a reaction temperature of 300 °C to 500 °C and a contact time of 2 s to 30 s, wherein the chromium-based catalyst is prepared by calcinating a catalyst precursor at a high temperature, the catalyst precursor is a mixture of a trivalent chromium compound and a metal powder, and based on the total mass of the catalyst precursor, the trivalent chromium compound represents 95 % to 99.9 % by mass, and the metal powder represents 0.1 % to 5 % by mass. in step one: pyrolysing dicyclopentadiene, as raw material, to obtain cyclopentadiene, with nitrogen or other inert gas as a diluent in a molar ratio of the diluent to dicyclopentadiene of 1: 0.5 to 3, wherein the pyrolysing is at a reaction pressure of 0.1 MPa to 1.5 MPa, a reaction temperature of 300 °C to 450 °C and a contact time of 5 s to 30 s; in step two: subjecting cyclopentadiene, as raw material, to a chlorination reaction in a liquid phase with chlorine to obtain 1,2,3,4-tetrachlorocyclopentane, in a molar ratio of chlorine to cyclopentadiene of 1 to 3: 1, wherein the chlorination reaction is at a reaction temperature of 0 °C to 40 °C, and a reaction time of 1 h to 10 h; in step three: subjecting 1,2,3,4-tetrachlorocyclopentane, as raw material, to a chlorofluorination reaction with hydrogen fluoride and chlorine in a gas phase in the presence of a chromium-based catalyst to obtain 1,2-dichlorohexafluorocyclopentene, in a molar ratio of 1,2,3,4-tetrachlorocyclopentane, hydrogen fluoride and chlorine of 1: 5 to 20: 5, wherein the chlorofluorination reaction is at a reaction pressure of 0.1 MPa to 1.5 MPa, a reaction temperature of 300 °C to 500 °C and a contact time of 2 s to 30 s, wherein the chromium-based catalyst is prepared by calcinating a catalyst precursor at a high temperature, the catalyst precursor is a mixture of a trivalent chromium compound and a metal powder, and based on the total mass of the catalyst precursor, the trivalent chromium compound represents 95 % to 99.9 % by mass, and the metal powder represents 0.1 % to 5 % by mass. <EOS>