The S136 mold steel samples with different Cr contents are fabricated by the selective laser melting (SLM) technique and the effect of Cr content on microstructures and performances of mold steels is investigated. The results show that the addition of Cr makes the numbers of voids, cracks and other defects in samples increase, which results in the reduction of relative density. With the increase of Cr content, the martensite content in the samples decreases first and then increases. Benefitting from the refinement of Cr, the higher the Cr content, the finer the microstructures of the samples, but the smaller the microhardnesses. The addition of Cr can generate a dense passivation film on the surface of samples to improve their anti-corrosion resistance. However, when the Cr content is too high, the corrosion resistance is reduced due to the increasing number of cracks.