Ni-base single crystal superalloys are metal alloys having excellent properties at high temperatures by uniformly forming fine cuboidal shaped Υ’ phase through heat treatment after single crystal casting. In general, it is known that the cooling rate of the solution heat treatment does not significantly affect microstructure and creep property because single crystal superalloys are sequentially subjected to solution heat treatment and aging heat treatment after single crystal casting. However, it was confirmed that the creep property of specific single crystal superalloys vary greatly depending on the cooling rate after solution heat treatment. In this study, solution heat treatment was performed by controlling the cooling rate of single crystal superalloy, and differences in lattice misfit of specimens subjected to aging heat treatment were compared and analyzed.  To accurately measure the lattice constant, a high-resolution XRD(X-ray diffraction) measurement method and an APT(Atom Probe Tomography) analysis method were used, and lattice misfits were calculated by comparing the respective results.  It was confirmed that the absolute value of the lattice misfit increased as the cooling rate increased, and this result coincided with the result that the creep property improved dramatically as the cooling rate increased.