The invention relates to a hydrothermal regeneration device of a waste white clay catalyst for a dimeric acid catalytic reaction, and a method thereof. The device is characterized in that the outer side of an inner kettle body is provided with a heat conduction medium jacket, the bottom of the inner kettle body is provided with a material outlet, the top of the inner kettle body is provided with a motor and a speed reducer, the output shaft of the speed reducer is connected with stirring paddles through a stirring shaft, and the motor drives the stirring paddles and a stirring support to rotate. Compared with other regeneration methods, the hydrothermal regeneration method adopted for oil and impurities in the waste white clay of the dimeric acid catalytic reaction catalyst has the following advantages: high-efficiency recovery of the oil from the waste white clay, the reservation of the microstructure of the white clay and the regeneration of surface active sites are realized, the recycling of the waste white clay is realized, added alcohols can directly volatilize without affecting the recovery of vegetable oil, the amount of the waste white clay is reduced through the regeneration of the waste white clay, the environment effect and the economic values of a dimeric acid synthesis technology are improved, and the method has good environmental meaning and economic values.