The invention discloses a rare earth oxide solid solution ceramic scintillator and a preparation method thereof. The main component of the ceramic scintillator is Gd2xLu2yY2(1-x-y-z)Eu2zO3 (the x is more than or equal to 0.1 and less than or equal to 0.6, the y is more than or equal to 0.1 and is less than or equal to 0.4, and the z is more than or equal to 0.01 and less than or equal to 0.1), and the ceramic scintillator has a crystal structure with a cubic Ia3 point group. Ceramic powder can be synthesized by a chemical coprecipitation method. The coprecipitation method adopts ammonia, ammonium hydrogen carbonate or a mixed solution of the ammonium water and the ammonium hydrogen carbonate as a precipitating agent, titrates the precipitating agent into a solution of gadolinium nitrate, lutecium nitrate, yttrium nitrate and europium nitrate to obtain a precipitate, and then the precipitate is dried and calcined to obtain nano-powder. The obtained powder is pressed into a ceramic blank through an isostatic compaction method, then the pressureless sintering is performed in vacuum or hydrogen atmosphere, the sintering temperature is between 1,600 and 1,900 DEG C, transparent Gd2xLu2yY2(1-x-y-z)Eu2zO3 ceramic can be obtained, a ceramic product with the needed dimension is prepared after the cutting, grinding and polishing, and the transmission rate of the ceramic in a visible region (400-800 nanometers) is more than or equal to 65 percent. The ceramic scintillator emits red light with a main wavelength of 610 nanometers under the excitation of ultraviolet light or X rays, and can be used for scintillating materials of imaging and detection of medical and industrial X rays.