In order to improve the efficiency of lung airway skeleton extraction, this paper introduces a new look-up-table (LUT) based thinning algorithm. This new approach consists of three major steps: the analysis and creation of the thinning model and the establishment of LUT based on above thinning model result. Thinning process by index-searching uses the LUT. Branch cutting based on the result of thinning obtains the final result. The usage of LUT index-searching during the thinning step transforms simple point judgments into LUT index search and has significantly improved the performance of the whole algorithm. Experimental results demonstrate that the new skeleton algorithm is 22.95 times faster than the existing thinning algorithm.