Abstract: The swinging angle of broken hammer in existing flding mechanisms is greater than 5 degrees, the work efficiency and service life of the broken hammer are seriously affected. In response to this problem, using the three special positions of the broken hammer, A new kind of broken hammer flding mechanisms is designed by using the drawing method. The mechanism can extend or retract the broken hammer in a straight line.The measures for adjusting the length of the rod-Ⅰand rod-Ⅱ are given. Take a type of broken hammer as an example, the broken hammer flding mechanisms is designed by the design approach is described in this article. In the post-200mm travel, angle variation of drill rod is 0.24 degrees, the maximum displacementthe of the top point of drill rod is 3.61mm along the radial direction of the drill rod, these indicators are meet the requirement of the broken hammer.