The invention relates to a synthesizing method for 2-chloronicotinic acid. The method includes the steps that 2-chlorine-3-chloromethylpyridine serves as a raw material, a sodium nitrite/organic acid system serves as an oxidizing agent, and under the condition that the reaction temperature ranges from 0 DEG C to 100 DEG C, the 2-chloronicotinic acid is obtained. The synthesizing method is mild in reaction condition, low in cost and high in 2-chloronicotinic acid yield, the used raw material is derived from a by-product of pesticide imidacloprid, and good social benefits and good economic benefits are achieved.