The invention discloses a method for etching to fabricate a black silicon layer by an aluminum-silicon eutectic thin film auxiliary drying method. The method comprises the steps of 1) providing a silicon wafer, and cleaning a surface of the silicon wafer; 2) recording a region, for fabricating the black silicon layer, on the silicon wafer as an operating region, and growing an aluminum-silicon eutectic thin film on a surface of the operating region by an electron beam evaporation coating process or a magnetron sputtering coating process; 3) selectively etching silicon in the aluminum-silicon eutectic thin film by a plasma etching process, and etching the silicon on the aluminum-silicon eutectic thin film; 4) taking aluminum resided on the aluminum-silicon eutectic thin film as a mask, and selectively etching the silicon on the operating region by the plasma etching process so that the black silicon layer is formed on the operating region; and 5) selectively etching the mask by the plasma etching process, etching the mask, and cleaning the black silicon layer. The method has the beneficial effects that the black silicon layer with favorable morphology can be fabricated.