A process for preparing an optically active derivative of 2-hydroxytetrahydrotiopyridine, wherein said derivative is 2- (2-acetoxy-6,7-dihydrothiene [3,2-c] pyridin-5 (4H) -yl) -2- ( (S) methyl 2-chlorophenyl) -acetate or a pharmaceutically acceptable salt thereof, comprising the following reactions: ** Formula ** wherein R 7 is a C 1-6 alkyl, trifluoromethyl, pentafluoroethyl, heptafluoropropyl, phenyl, or a Z-substituted phenyl, wherein Z is a C1-3 alkyl, halo, cyano, nitro or trifluoromethyl and is in the 2, 3 or 4 position of the phenyl ring； specifically comprising the following steps: (1) reacting a compound of formula II with a compound of formula III or a salt thereof in the presence of a base, to obtain a compound of formula IV or one of its salts, where the solvent used is one or more selected from benzene, toluene, chloroform, n-hexane, cyclohexane, dichloromethane, 1,2-dichloroethane, methyl t-butyl ether, carbon tetrachloride, ethyl acetate, propyl acetate, butyl acetate, methanol , ethanol, acetone, tetrahydrofuran, diethyl ether, acetonitrile, N, N-dimethylformamide or dimethyl sulfoxide； the base used is selected from triethylamine, diisopropylethylamine, 1,8-diazabicyclo [5,4,0] undec-7-ene, potassium carbonate, sodium carbonate, potassium bicarbonate or sodium bicarbonate； the reaction temperature ranges from -20 ° C to 100 ° C； and the salt of the compound of formula III is selected from hydrochloride, p-toluenesulfonate, acetate, sulfate, phosphate, trifluoromethanesulfonate, oxalate, methanesulfonate, benzenesulfonate or hydrobromide； and (2) reacting the compound of formula IV or one of its salts with a compound of formula V or a compound of formula VI in the presence of a base, to obtain the compound of formula I； wherein the reaction solvent employed is one or more selected from benzene, toluene, chloroform, n-hexane, cyclohexane, dichloromethane, 1,2-dichloroethane, methyl t-butyl ether, carbon tetrachloride, ethyl acetate, propyl acetate, b
