The plasma radiant intensity was investigated by a laser micro-plasma spectral analysis system. The system consists of an YJC- Ⅱ laser micro-spectral analyzer and a CCD data acquisition and processing system. National standard soil samples were studied in the experiment under different ambient atmosphere with argon, helium and the mixture of argon and helium by using the analysis lines, CaⅡ 393. 367 nm and Ca Ⅱ 396. 847 nm. The results of this research suggest that both the time of plasma illumination and the radiant intensity of plasma in an atmosphere of helium argon mixture were better than that in pure helium or argon gas. The plasma radiant intensity was obviously enhanced when the proportion of helium and argon was 66. 7% and 33.3%, respectively. Under these conditions, the influence of the height of auxiliary electrode on laser micro-plasma radiant intensity was also investigated. The maximum laser micro-plasma radiant intensity was reached when the height of auxiliary elec trode was 3 mm.