The invention discloses a method for preparing high-yield carbon quantum dots, which comprises the following steps that: (1) ammonium citrate is put into an electric heating furnace, the temperature rises at a heating rate of 5 to 50 DEG C/min, and the reaction is carried out for 2-4h at a temperature of 150 to 250 DEG C to obtain a pyrolysis product; (2) the pyrolysis product is milled into powder and added with ethanol to be stirred and centrifuged to remove insolubles to obtain a brown ethanol solution containing carbon quantum dots; and (3) the drying is carried out to obtain the carbon quantum dots. The process is simple to operate, the source of raw materials is wide, the cost of raw materials is low, the preparation conditions has low requirements and are relatively mild, the yield of obtained carbon quantum dots and the quantum yield are higher, the problems that the carbon quantum dots can not be produced on the scale and the fluorescence quantum yield of the obtained carbon quantum dots is low due to the limit of the process and the raw materials in the traditional preparation method of the carbon quantum dots can be solved, and the method can be applied to the fields such as biomarker, bio-imaging, a photovoltaic device, and a biosensor.