The invention relates to a self-adaption follow fixture device for car seat sliding rail assembling. The self-adaption follow fixture device comprises driving mechanisms, an unlocking mechanism and a follow fixture; and the driving mechanisms are fixedly installed at the fixing positions on a peripheral sliding rail assembling production line side by side at intervals in the left-right direction, the unlocking mechanism is provided with a displacement sensing system, and the follow fixture is arranged between the driving mechanism and the unlocking mechanism in the manner of being capable of moving in the front-and-back direction. The follow fixture comprises a fixture tray, a guide rail installation plate, a workpiece positioning base, a measurement contact block, a lead screw nut pair and a locking unit. According to the self-adaption follow fixture device, collineation assembling of different sliding rails is achieved, the using rate of an assembling line can be effectively improved, the complexity of all technological equipment can be effectively reduced, the assembling quality can be effectively improved, and the good cost performance of the technological equipment can be effectively obtained.