An attempt is made to research how does the laser processing parameters impact the width of melted zone in the high carbon alloy steel Cr12 surface using Nb:YAG laser as a heat generating source.The microstructure and chemical composition distribution of Cr12 steel after laser-remelting are observed and analyzed by using optical microscopy, scanning electron microscopy(SEM)and energy spectrometer(EDS). Different widths of melted zone, which are processed by different laser processing parameters, are measured. Hardnesses of laser melted zone are also investigated. The results show that Cr12 steel gets three layers structures, including the melting zone, heat affected zone and the matrix. The microstructure of melted zone has very fine equiaxial crystal and columnar crystal, which eliminats the impurity phase, and the alloying elements are evenly distributed after laser-remelting process. The microhardness of heat affected zone is improved significantly, and the width of melted zone changes along with laser parameters variation and defocusing distance has the most effect on the width of melted zone.