The microstructure distribution, surface hardness and residual stress of the 40Cr, which is modified by single - line solidification and folded - line solidification, are studied in this article. It is indicated that the surface micro-structure of the material treated by single - line laser solidification, is comprised of surface melting zone, sub - surface phase hardened zone and high temperature annealed zone connected with substrate. The difference between the folded - line laser solidification and the single - line solidification are the surface hardness and microstructure of the annealing region and secondary - hardened region. And the test of residual stress indicates that: in single - line laser rapid solidification, the maximal residual stress, which is pulling stress, emerges on the central line of the solidification zone. On the margin of melting zone, there exists compressive stress and in the heat affected zone there is pulling stress again. The residual stress of the folded - line solidification,and the later solidification zones bring stress on the former solidification zones and furthermore tempered the former ones.