The 18Ni300 die steels were prepared by the Selective Laser Melting (SLM). Compared with the forged sample, the microstructure and corrosion resistance of 18Ni300 die steel sample prepared by SLM in 3.5% (mass fraction) NaCl solution was analyzed. The results show that the hardness of the SLM formed specimen is slightly lower than that of the forged specimen. There were many small holes in the microstructure of SLM sample; the volta potential of SLM formed sample is lower than that of forged sample; the corrosion resistance of SLM formed sample is worse than that of forged sample according to the results of the polarization curve test and immersion corrosion test.