The utility model discloses a forming device for thermal expansion auxiliary prepregs of silicon sheets. The device comprises an upper mould, a lower mould and the silicon sheets. The silicon sheets are attached into mould cavities of the upper mould and/or the lower mould. Preferably, mould release agent layers are coated in the mould cavities of the upper mould and the lower mould, and the silicon sheets are attached onto the mould release agent layers in the mould cavities of the upper mould and/or the lower mould. Compared with the prior art, the forming device has the advantages that by the aid of thermal expansion of silicon, the silicon sheets uniformly expand and generate internal pressure in a heating-forming process, prepreg sheets uniformly pressed in all directions, accordingly, the lateral face of a product is also sufficiently and uniformly pressed, and high layer-to-layer bonding strength is obtained.