This invention use 2,5- dimethyl pyrazine as raw materials, selectively synthesize 5-methyl pyrazine-2-carboxylic acid. Its technology is use 2,5 - dimethyl pyrazine as raw material, through oxidation of nitrogen and hydrogen peroxide, acetic anhydride acid oxidation, hydrolysis and oxidation process, gain 5-methyl pyrazine-2-carboxylic acid. HPLC analysis of their content is over 99%, with 0.1 mol / L of sodium hydroxide titration, content is not less 98%, melting point is not less than of 163 deg, the quality of medicine to meet glipizide, Acipimox requirements. The process is scheme simple, high-yield, low cost and suitable for industrial production.