The invention discloses a carbon-nitrogen catalyst for photosynthesizing hydrogen peroxide and a preparation method thereof. The preparation method comprises the following steps of: roasting organic matter powder containing carbon and nitrogen in air or inert atmosphere to obtain C3N4 solid powder; then grinding the C3N4 to mix with sugar liquid, and carrying out carbonation reaction in a hydrothermal reactor to obtain C3N4 modified by amorphous carbon; and then roasting in the inert atmosphere to obtain the carbon-nitrogen catalyst (CxNy). The adopted materials are rich in source, is non-toxic, has the characteristics of being environmentally friendly and sustainable and being low in cost, and is suitable for large-scale production. The carbon-nitrogen catalyst is used for producing H2O2 by using water, oxygen and a little amount of alcohol and utilizing sunlight as an energy donor, the whole process does not use any toxic reagent and toxic solvent, has no emission of wastes and waste water, is mild in reaction condition and is environmentally friendly and free of pollution.