Expansion tool capable of achieving butt joint and operation method of expansion tool

The invention provides an expansion tool capable of butt joint and an operation method thereof, the outer wall of the tail end of an oil pipe or a drill rod string is in threaded connection with the inner wall of the head end of a central pipe, a reducing section is formed on the outer wall of the upper part of the central pipe, an expanding section is formed below the reducing section, an anchor block is mounted in the expanding section, an anchor sleeve is mounted on the central pipe below the anchor block, and the anchor sleeve is in threaded connection with the central pipe. The outer wall of the tail end of the anchor sleeve is in threaded connection with the inner wall of the head end of the outer cylinder, a spring cavity is formed between the outer wall of the center pipe and the inner wall of the outer cylinder, a spring is arranged in the spring cavity, and the inner wall of the tail end of the center pipe is in threaded connection with the outer wall of the head end of the insertion pipe. The inser