The invention discloses a dehydration C-alkylation method for a heterocyclic methyl compound. According to the method, alcohol is used as an alkylation reagent and undergoes dehydration C-alkylation with the heterocyclic methyl compound without presence of a catalyst so as to synthesize an alkylated heterocyclic compound; meanwhile, alcohol and the heterocyclic methyl compound can be directly subjected to dehydration C-methyl alkylation reaction at methyl position in the presence of air and alkali, wherein the reaction temperature is 100 to 180 DEG C; the reaction time is 6 to 60 hours; the reaction solvent is an organic solvent; and a byproduct is water. According to the method, cheap, easily and widely available and stable alcohol with low toxicity is used as the alkylation agent; no catalyst is used; and the alkylated compound is directly synthesized via the dehydration C-alkylation reaction in the presence of air and alkali. The method provided by the invention has low demand for reaction conditions, a wide application range and certain research and industrial application prospects.