The influence of different shielding gases on microstructure and property of laser welded joint is studied by the weld test of microalloyed C-Mn steel. The results show that, under the same condition of laser weld heat input, full-penetration weld seams can be obtained by three different shielding gases of N2, Ar and air, but the sags in the weld zone shielded by N2 are the most obvious. The microstructures of the weld zone are mainly lath martensite. In the weld seam formed in the air, there are a few acicular ferrites, the number of inclusions is more than that shielded by N2 and Ar, and the ratio of large scale inclusion is relatively high. In all three cases, the mean microhardness and tensile strength of the welded joint are higher than that of the base metal, while the mean microhardness of the weld seam in the air is smaller than that when shielded by N2 or Ar.