The invention relates to an automatic crab trap releasing device. Problems of great labor intensity, high cost and low efficiency caused by manually releasing the traditional crab trap are mainly solved. The automatic crab trap releasing device comprises a fixed seat and an unhooking device, wherein a lifting hook comprises a clamping part and a releasing part; a crab trap is connected with a supporting rope through the lifting hook; the unhooking device is hinged on the fixed seat; the unhooking device comprises a bottom plate, a stopping plate and a stopping block; a unhooking slot is formed in the bottom plate; the unhooking slot comprises a sliding-in end and a releasing end; the stopping block is fixedly connected with the bottom plate; a clamping slot is formed in the stopping block; the lifting hook is in clamping fit with the clamping slot; the supporting rope is connected with the releasing part; the releasing part of the lifting hook is pulled by the supporting rope to slide into the unhooking slot; the clamping part of the lifting hook is pushed in the clamping slot so as to drive the unhooking device to rotate for a certain angle around a hinging center; the supporting rope is separated from the lifting hook through a rope releasing opening; and the lifting hook is released from the unhooking device. As the releasing device can be used for releasing the crab trap, the automatic crab trap releasing device provided by the invention is advantaged in that the labor intensity of the releasing device is low, the cost of the device is saved, the production effect of the device is extremely high, and automatic separation is effectively realized.