Blanket is the key energy conversion component of a fusion reactor, it is designed with a large number of complex embedded cooling channels to remove the high nuclear heat deposition. Due to the complex inner-channeled structure, the fabrication of the blanket components has been one of the key issues of the blanket technical development. In this study, the selective laser melting (SLM) additive manufacturing (AM) processing was employed to fabricate small scale test blanket module with China low activation martensitic (CLAM) steel, and the hot isostatic pressing (HIP) was applied to improve the microstructure and mechanical properties. The microstructure and mechanical properties of the SLM built CLAM at the as-built, standard heat treatment (SHT) and HIP&SHT status were investigated and evaluated. The results showed that the relative density at the as-built status compared to the hot-rolled CLAM steel reached 99.7%. The tensile strength of the as-built status was 966.2 MPa and 829.1 MPa in the directions vertical and parallel to the building direction, respectively. After the HIP&SHT, the orientation of the microstructure and the difference in strength in different directions decreased. The strength values in the directions vertical and parallel to the building direction were similar, which were equivalent to that of the hot-rolled CLAM steel with SHT. Moreover, the impact absorbed energy in the directions vertical and parallel to the building direction was increased from 21.02 J to 9.18 J at the as-built status to 54.48 J and 18.83 J at the HIP&SHT status, respectively. Meanwhile, micro-defects were drastically decreased with the help of HIP. It could be concluded that the dislocation migration and recrystallization in HIP process is effective to improve the microstructure and mechanical properties of the SLM built CLAM steel. (C) 2018 Elsevier B.V. All rights reserved.