Abstract: In order to solve the problem of high labor intensity, low efficiency and easy to cause safety hidden trouble of workers in the process of drilling of truck-mounted drilling machine, a fully hydraulic automatic rod changing device was developed. Through lifting device, the drill pipe is lifted to the tray of the drill pipe of feeding drilling rig. The drilling rig, the base and the clamping device cooperate with the power head of the on-board drilling machine to complete the work of adding and removing the drill pipe. The control board is installed on both sides of the translational leg of the base, forming a functional segmentation and achieving the reduction of staff and the increase of efficiency. In order to solve the problem of the burning joint between the active joint of the power head and the drill pipe in the field industrial test, the optimal design of the gripper was carried out. Two degrees of freedom (left and right, upper and lower) of clamping device were added, which constituted three degrees of freedom of floating between the active joint of power head and the joint of drill pipe in the process of upper fastening, and solved the problem of wire fastening sintering.