The invention discloses a method for preparing a YAG-based multilayer composite transparent ceramic by using Isobam gelcasting. The prepared multilayer ceramic satisfies a structure shown by a following formula: YAG/Re:YAG/YAG or YAG/Re: YAG/Re:YAG, wherein the YAG layer is composed of Y3A15O12, the Re:YAG layer is composed of (Y<1-x>Re<x>)<3>A<15>O<12>, x is more than or equal to 0.02 and is lessthan or equal to 0.2; Re is one of rare earth elements of cerium, praseodymium, neodymium, samarium, europium, terbium, dysprosium, holmium, erbium, thulium or ytterbium. The method comprises the steps that firstly Isobam gelcasting slurry is prepared, then the slurry is defoamed and is cast into a mold, after a first layer of the slurry gel is cured, the other layer of slurry is poured, the slurry is completely gelled, drying treatment is conducted, and the gel is discharged; biscuit after discharging the gel is vacuum sintered and annealed, and after double-sided polishing, the multilayer composite transparent ceramic is obtained. The method provided by the invention is mainly water-based slurry, green and environmentally friendly, and the obtained ceramic has the characteristics of high density, complicated structure, good optical quality, high transmittance, small interfacial ion diffusion range, and the method is very suitable for the preparation of the large size and composite YAG-based transparent ceramic material.