The conversion of biomass into biofuel using solvents that come from biomass itself is being more and more important for the concern of renewable development and CO2 netural. Formic acid was used as an in situ hydrogen donor for the liquefaction of wheat straw alkali lignin. It was found that the addition of ethanol improved the yield of monophenols remarkably. Although ethanol exhibited a poor effect in the liquefaction of lignin, it was found to be a good assistant solvent for improving the monophenol yield of the formic acid system significantly.