A method for preparing 2,3-dichloro-5-trifluoromethylpyridine, wherein the method comprises: at a temperature of 100~150°C and a pressure of 0.5-5.0 MPa, in presence of a first catalyst, 2-chloro-5-trifluoromethylpyridine reacts with chlorine gas to obtain 2,3-dichloro-5-trifluoromethylpyridine; the first catalyst is at least one selected from supported metal chloride, supported zeolite molecular sieve and supported heteropolyacid; for the supported metal chloride, its active components are at least one selected from WCl 6, MoCl 5, FeCl 3, AlCl 3, CuCl 2, ZnCl 2, SnCl 4, and SbCl 5, and the load of the active components is 1~50wt%; for the supported zeolite molecular sieve, its zeolite molecular sieve is at least one selected from ZSM-5, Beta, X, Y, 5A and L type zeolite molecular sieve, and the load of the zeolite molecular sieve is 1~50wt%; for the supported heteropolyacid, its heteropolyacid is at least one selected from phosphotungstic acid, silicotungstic acid, phosphomolybdic acid and silicomolybdic acid, and the load of heteropolyacid is 1~50wt%; the 2-chloro-5-trifluoromethylpyridine is prepared by the following steps: chlorofluorination reaction: in presence of a catalyst for chlorofluorination, the chlorofluorination temperature is maintained at 150∼320°C, and 3-methylpyridine, chlorine gas and hydrogen fluoride are introduced into a chlorofluorination reaction region, to obtain a mixed gas comprising 3-trifluoromethylpyridine; chlorination reaction: in presence of a chlorination catalyst, the chlorination temperature is maintain at 220~380°C, and the mixed gas comprising 3-trifluoromethylpyridine obtained in step is introduce into a chlorination reaction region, to obtain 2-chloro-5-trifluoromethylpyridine, the chlorination catalyst is selected from fluoride, oxide, hydroxide, carbonate or chloride of magnesium, calcium, barium, a supported palladium catalyst supported on activated carbon, alumina or aluminium fluoride. at a temperature of 100~150°C and a pressure of 0.5-5.0 MPa, in presence of a first catalyst, 2-chloro-5-trifluoromethylpyridine reacts with chlorine gas to obtain 2,3-dichloro-5-trifluoromethylpyridine; the first catalyst is at least one selected from supported metal chloride, supported zeolite molecular sieve and supported heteropolyacid; for the supported metal chloride, its active components are at least one selected from WCl 6, MoCl 5, FeCl 3, AlCl 3, CuCl 2, ZnCl 2, SnCl 4, and SbCl 5, and the load of the active components is 1~50wt%; for the supported zeolite molecular sieve, its zeolite molecular sieve is at least one selected from ZSM-5, Beta, X, Y, 5A and L type zeolite molecular sieve, and the load of the zeolite molecular sieve is 1~50wt%; for the supported heteropolyacid, its heteropolyacid is at least one selected from phosphotungstic acid, silicotungstic acid, phosphomolybdic acid and silicomolybdic acid, and the load of heteropolyacid is 1~50wt%; the 2-chloro-5-trifluoromethylpyridine is prepared by the following steps: chlorofluorination reaction: in presence of a catalyst for chlorofluorination, the chlorofluorination temperature is maintained at 150∼320°C, and 3-methylpyridine, chlorine gas and hydrogen fluoride are introduced into a chlorofluorination reaction region, to obtain a mixed gas comprising 3-trifluoromethylpyridine; chlorination reaction: in presence of a chlorination catalyst, the chlorination temperature is maintain at 220~380°C, and the mixed gas comprising 3-trifluoromethylpyridine obtained in step is introduce into a chlorination reaction region, to obtain 2-chloro-5-trifluoromethylpyridine, the chlorination catalyst is selected from fluoride, oxide, hydroxide, carbonate or chloride of magnesium, calcium, barium, a supported palladium catalyst supported on activated carbon, alumina or aluminium fluoride. chlorofluorination reaction: in presence of a catalyst for chlorofluorination, the chlorofluorination temperature is maintained at 150∼320°C, and 3-methylpyridine, chlorine gas and hydrogen fluoride are introduced into a chlorofluorination reaction region, to obtain a mixed gas comprising 3-trifluoromethylpyridine; chlorination reaction: in presence of a chlorination catalyst, the chlorination temperature is maintain at 220~380°C, and the mixed gas comprising 3-trifluoromethylpyridine obtained in step is introduce into a chlorination reaction region, to obtain 2-chloro-5-trifluoromethylpyridine, the chlorination catalyst is selected from fluoride, oxide, hydroxide, carbonate or chloride of magnesium, calcium, barium, a supported palladium catalyst supported on activated carbon, alumina or aluminium fluoride.