The invention provides a piston take-out device for a hydraulic anchor of an RTTS packer and an application method. The device comprises a locking mechanism, a connecting part, a round bar and a punchhammer, wherein the connecting part is provided with two parallel surfaces, one of which is provided with a T-shaped groove and is slidably connected to the locking mechanism through the T-shaped groove, and the other surface of which is provided with the round bar vertically and fixedly, the round bar penetrates through the punch hammer, and can reciprocate in the punch hammer; the locking mechanism comprises two locking blocks connected through a bolt, one ends of the locking blocks are inserted into small holes of the piston while the other ends of the locking blocks are slidably connectedto the connecting part; the locking blocks are provided with positioning through holes in the sliding directions; inner threads are arranged in the positioning through holes; and bolts penetrate through the positioning through holes; and the distance between the two locking blocks is adjusted through the threads. The piston take-out device provided by the invention is simple in structure and convenient to use, the labor intensity is reduced effectively, and the maintenance efficiency of the RTTS packer is improved.