Lower detection accuracy restricts the development of laser induced b reakdown spectroscopy (LIBS). A partial least square (PLS) method is proposed to analyze the Pb content in pot atoes by LIBS.The PLS model is composed of two steps which include different smoothing points and standard nor mal variate transformation (or multiple scatter correction,or the mean centralized,or the first derivative of denoising,or second derivative of denoising),to pretreat the LIBS spectrum.Spectral data of the 96potatoes samp les are pretreated by different data smoothing from 3points to 17points.The samples of potatoes are pretreat ed by acid wet digestion,and the real content of Pb is obtained by atomic absorption spectrophotometer (AAS).Th e LIBS spectrum chooses the 401－417nm wavelength range which contains characteristic spectral lines of Pb.The main evaluation indexes of PLS models,such as correlation coefficient,root mean squared error of cross-va lidation and root mean square error of prediction,are compared and analyzed.The obtained three indexes of PLS model after 13points smoothing and processing of the mean center are reach 0.9963,6.4and 11.5,respectively.In one word,the calibration and prediction of t his quantity model are the best results.Select ing the appropriate data for preprocessing can effectively improve the quality o f agricultural products detected by LIBS.