It was investigated that micro-cracks and microstructure characteristics of GH3230 superalloy fabricated by selective laser melting (SLM) before and after hot isostatic pressing (HIP) in order to reveal the SLM additive formability of GH3230 superalloy. The results show that there are many solidification micro-cracks in the SLM as-deposited GH3230 superalloy, and the micro-crack distribution is netlike along the XOY section and is threadlike along the ZOY section. Most of the solidification micro-cracks can be eliminated by HIP, and some longer micro-cracks are difficult to eliminate. There is elemental segregation phenomenon in as-deposited GH3230 superalloy fabricated by SLM, and exist a small amount of carbides along the boundary. After HIP, a large number of secondary carbides of MoWCr alloying elements are precipitated and the carbides along the boundary are larger than the intracrystalline precipitated ones. Micro-cracks easily reduce the XY direction tensile strength and elongation of as-deposited GH3230 fabricated by SLM and the XY direction tensile strength and elongation is greatly improved by HIP, and the effect mechanism was made a preliminary analysis.