In order to overcome the shortage of the large variation of spectrum intensity in Laser Induced Breakdown Spectroscopy (LIBS) and to improve the measurement accuracy in term of the relative standard deviation of the line intensity from repeating measured spectrum, an auto-focusing system is integrated into the LIBS technique and used to control the size and position of the laser focus on the sample surface. Based on the gray level difference analysis method and a modified hill-climbing algorithm, an auto-focusing system, including hardware and software, is developed and used to automatically locate the laser focus point and then adjust the sample positions in LIBS measurements. The RSD of the repeating measurements is then improved.