The research aims to set up the determination method of heavy metals in tobacco by ICP—MS and analyze its uncertainty. Microwave digest technique is used for decomposition of the tobacco samples. Bi, Sc, Ge and In are employed as internal standards to eliminate the interference of the matrix. A method is developed for simultaneous determination of Cr, Cu, As, Cd, Hg and Pb in tobacco from Yunnan Province by ICP—MS, and the measurement uncertainty is evaluated by metrological method. The test results indicate that in the content range of 0—1. 0 g/ml, the linearly dependent coefficient of six elements is 1. 0000, and the RSD achieves 1. 5%—11% (n=8). The elemental content in tobacco is as follows: Cr (2.92,0.24) mg/kg, Cu (3.64,0.24) mg/kg, As (0.467,0.025) mg/kg, Cd (3.12,0.15) mg/kg, Hg (0.035, 0.006) mg/kg, Pb (4.62,0.36) mg/kg. The uncertainty of sample size, the constant volume of the sample solution can be neglected. It is concluded that the method is accurate, simple, sensitive and rapid.