The invention discloses a preparation method of trans-1, 2-dichloro-3, 3, 3-trifluoropropene. The method comprises the following steps: a, 1,1,1,2,2,3-hexachloropropane and / or 1,1,1,2,3,3-hexachloropropane are reacted with the existence of
diluent gas and a catalyst, a gas-
phase reaction is carried out for removing
hydrogen chloride, and 1,1,2,3,3-pentachloropropene is produced; b. a
liquid phase fluoridation reaction is carried out between 1,1,2,3,3-pentachloropropene and
hydrogen fluoride with the existence of a
liquid phase fluorination catalyst, or a
gas phase fluorination reaction is carried out between 1,1,2,3,3-pentachloropropene and
hydrogen fluoride with the existence of a
gas phase fluorination catalyst; c. washing, alkali washing and
drying are carried out for reaction products in the step b, and trans-1, 2-dichloro-3, 3, 3-trifluoropropene is obtained by rectification in a condition with normal pressure. The method has the characteristics of high reaction selectivity, high conversion rate and high
stereoselectivity, and is mainly used for preparing trans-1, 2-dichloro-3, 3, 3-trifluoropropene.