The invention relates to a method for preparing Re:YAG polycrystalline transparent ceramic by using different molding modes, which adopts commercial high-purity Y2O3, Al2O3 and Re2O3 as raw materials, adopts MgO, CaO or TEOS (tetraethyl orthosilicate) as sintering additive, and prepares a raw blank by a cold isostatic pressing, slip casting or tape casting process to react and sinter the transparent polycrystalline Re:YAG ceramic. The method comprises the following steps: mixing and adding the oxides into a liquid medium; adding a certain amount of dispersant, adhesive, plasticizer, pressing agent and defoaming agent, carrying out ball milling, and mixing; treating the slurry under different conditions in different molding modes to obtain the raw blank; and sintering the degreased raw blank in a vacuum furnace. For the Re:YAG ceramic sintering body with thickness of 1.5mm, the transmission rate of straight light in the wavelength of 1064nm is not lower than 80% after the Re:YAG ceramic sintering body is subjected to double-sided polishing. For the raw blank which is prepared by different molding modes and is sintered for 10 hours at 1750 DEG C, sizes of ceramic grains are different, wherein regarding the raw blank prepared by cold isostatic pressing, the average grain of the ceramic is 13.5mu m; regarding the raw blank prepared by slip casting, the average grain of the ceramic is 3.5mu m; and regarding the raw blank prepared by tape casting, the average grain of the ceramic is 1.5mu m.