The effects of solidification rate on the microstructure of a Ni-based superalloy were investigated by zoom melting liquid metal cooling (ZMLMC) unidirectional solidification. The temperature gradient was approximately constant. It is revealed that with the increase of solidification rate, the dendrite structure is refined, and both the primary dendrite spacing λ1 and the secondary dendrite spacing λ2 are reduced, they show a linear relationship with v-1/4 and v-1/2, respectively. The sizes of γ' precipitates decrease with increasing of solidification rate, and the shapes turn to be regular. At the same rate, the γ' phase in interdendrite area is larger and more irregular than that in dendrite area. The γ/γ' eutectic also becomes smaller and more dispersed with the increase of solidification rate, but the total volume proportion remains stable