In terrorist attacks, explosive attacks are the most common terrorist attacks. Explosive attacks have seriously threatened the daily life of the public, so the detection of explosives has attracted increasing attention. Through laser-induced breakdown of RDX and TNT at atmospheric pressure and low pressure, it was found that two characteristic spectral lines of atomic lines and molecular lines, CN (421.3 nm) and C₂ （516.2 nm）, were the most valuable among all the spectral lines of organic explosives. The results show that the spectral line intensity is related to atomics proportion and molecular structure of the sample, and molecular lines are more valuable than atomic lines. Compared with the atmospheric pressure, the relative standard deviation of RDX decreases from 5.1% to 1.8%, and the relative standard deviation of TNT decreases from 15.7% to 2.7% under low pressure. A low pressure environment can effectively improve the analytical precision of LIBS to detect organic and increase the accuracy of spectral analysis, which helps LIBS to improve the detection and analysis precision of organic explosives.