According to extracting the center coordinate of spot in an oil film thicknes s measurement system with differential laser triangulation,based on the analysi s on spot image features of ceramic gauge block and oil film,a method of spot po sitioning is presented with cross correlation and improved Gaussian fitting.The s mooth and feature reserved spot image is obtained through the correlation operat ion of the spot image and a Gaussian mask image.The center coordinate of the sp ot image is obtained by improved Gaussian fitting with the ascending edge and de scending edge data of the correlation results extracted for fitting.To verify th e performance of the method,experimental measurement is carried out with differ ent spot center extraction methods.Compared with square weighted centroid met h od,Gaussian fitting method,improved Gaussian fitting method and cross correlat ion Gaussian fitting method,the precision of the presented mothod is higher.The experiment of oil film spot center extraction is carried out.The results show th at the algorithm presented is feasible for oil film thickness measurement system with differential laser triangulation.