The invention provides a method for preparing ultrathin crystalline silicon double-sided solar cell. The method comprises steps of: firstly thinning a polycrystalline silicon substrate to 90-120[mu]mat 18-25 degrees centigrade for 2000-2300s by using a mixed solution of HF, H2O2 and an additive, wherein a textured structure is formed on the surface of the substrate during the thinning process; preparing a PN junction by roll diffusion, and using ultrasonic atomization of phosphoric acid, thereby being nontoxic and nonpolluting, and achieving a uniform diffusion junction; and disposing siliconnitride antireflection layers on the front and back sides of the substrate; finally forming finger electrodes on the front and back sides by a silk-screen printing and sintering process. The method is suitable for the production technology of polycrystalline silicon 90-120[mu]m thick. Compared with a method for preparing a conventional polycrystalline silicon cell 180[mu]m thick, the method can reduce the thickness of the cell under the premise of ensuring a fragmentation rate, ensures battery efficiency, is simple in process, and low in cost. The method also solves the problem that the thincell is likely to be bent and is fragile, and can be industrialized by experimental verification.