Abstract: The calibration curve method was used to carry out quantitative measurement and uncertainty evaluation of Mn and Si, the common trace elements in low alloy steels, in micro area by electron probe microanalysis. The results show that when the inclusion factor k=2, the mass fraction of Mn in the sample was 0. 12%, and the expanded uncertainty was 0. 004 8%. The mass fraction of Si element was 1. 36%, and the expanded uncertainty was 0. 042%.