Formic acid (FA) is an important material in the chemical industry. Currently, FA can be produced either from fossil fuel or biomass, the latter being much more sustainable than the former. The methods of catalytic oxidation of biomass in aqueous solutions under oxygen (O-2) using catalysts is promising, since the conditions are mild, the purity of produced FA is high, and the catalysts can be reused. The catalysts include V-containing heteropoly acids (HPAs), ionic liquid (IL)-HPAs, NaVO3, VOSO4, FeCl3, solid catalysts, and catalyst complex. In this review, we introduce the methods of oxidation of biomass to FA in these catalysts or catalyst systems, oxidation conditions, mechanism of biomass to FA, the relationship of catalytic hydrolysis and catalytic oxidation during the oxidation of biomass to FA, suppression of carbon dioxide (CO2), and improvement of FA yield. Lastly, we analyze problems and perspectives of current methods of O-2 oxidation of biomass to FA in aqueous solutions.