The main purpose of this study was to develop a method that can optimize the algorithm for puncture point calculation, and therefore improve the accuracy of X-ray guided breast biopsy. The proposed method is: first, select two guiding points; then, use the guiding points to construct X-ray cone-beams, so the joining section of the cone-beams can be used to determine the puncture target point. The method was verified by a phantom emulation, in which the calculated target-points were all found within the central part of the target lesion, and far away from the boarder of the lesion (change the x-ray tube angle by 15° would only cause a slight deviation no more than 1.4 mm), the accuracy is enough to fulfill the needs of biopsy operation. This study also found out that, the shorter the distance between the guiding point and the center of the lesion's project, the nearer the calculated biopsy-point will be to the actual lesion center.