The invention discloses an etching method for the diffusion layer of a crystalline silicon solar battery sheet. First, the silicon sheet that has been diffused and doped is put into a tubular thermal oxidation furnace, and a silicon sheet is deposited on the front side of the silicon sheet by a chemical vapor deposition method. layer of silicon dioxide film; place the silicon chip in the mixed solution of phosphoric acid and nitric acid to fully react the silicon chip with the solution, wherein the molar ratio of phosphoric acid to nitric acid is phosphoric acid: nitric acid = 2-5:10; Put the chip into hydrofluoric acid solution, remove the silicon dioxide film layer on the surface of the silicon chip, and then rinse it with deionized water. The etching method of the invention has the advantages of simple process, low equipment requirements, easy monitoring of the etching process, high production efficiency, and can effectively reduce the number of low-efficiency cells caused by etching.