The invention discloses a preparation method of 2,3-dichloropyridine. The preparation method is implemented by taking 2,3,6-trichloropyridine as a starting material and dissolving the 2,3,6-trichloropyridine into an solvent, taking an organic compound as a hydrogen donor and heating the organic compound in the presence of a metal catalyst until a micro reflux reaction occurs, carrying out post-treatment on reaction liquid so as to obtain a target product 2,3-dichloropyridine, wherein the solvent is a C1-C4 alcohol solvent; the hydrogen donor is of a structure shown in a formula (VI), wherein R refers to H<+1>, Na<+1> and NH<4+>; and the metal catalyst is a Pd/C catalyst. According to the invention, a CTH reaction is successfully applied to the dechlorination and hydrogenation of multiple chloropyridines, the catalyst can be repeatedly regenerated and continuously indiscriminately used, the hydrogen donor is relatively cheap, available and stable, nontoxic and easily removed from a system, the yield of target products is good, a small amount of by-products are extensive in use, chloropyridine raw materials with a high economic value are fully used, the operation steps are simple, and the preparation process is safe, green and environmental-friendly.