The invention discloses an automatic dismounting device for a plugging rubber cap of a liquid accumulator, and relates to the field of automation, the automatic dismounting device comprises a feeding slide way, a discharging slide plate, a dismounting air cylinder, dismounting assemblies and a discharging mechanism, the discharging slide plate is fixedly connected to the front end of the feeding slide way, and the dismounting assemblies are arranged on the two sides of the discharging slide plate; the disassembling assembly is connected to an output shaft of the disassembling air cylinder, and the disassembling air cylinder is automatically triggered to work after the liquid storage device falls in place and collides with the first button, so that automatic action is achieved, and idle running of the machine when no material exists is avoided. And meanwhile, after the disassembly air cylinder is reset, the collision table collides with the wood block, the wood block is stressed to touch the second button, then the lifting air cylinder is started to act once, one liquid storage device is discharged, and the phenomenon that machining is missed due to the fact that materials are discharged when the disassembly air cylinder is not reset is avoided.