The directional solidification experiment of SRR99 Ni-based superalloys is conducted by the selective laser melting (SLM) method, and the microstructure, the phase composition, the element segregation of samples are measured. The results show that a good metallurgical combination between the deposition layer and the as-cast substrate is formed, and the deposited samples are composed of the γ and γ′ phases. There is a strongest diffraction peak both in the deposition layer and the as-cast substrate when the diffraction angle is 50.78°, which indicates that the growth orientation of the substrate gets well extended in the SLM deposition structure. The primary dendrite spacing is only 1-2 μm and the secondary dendrite arm degenerates and even disappears. The segregation ratio of each alloy element is close to 1 and the elements are uniformly distributed at the dendrite arms and the interdendritic space.