A modified Ostwald ripening theory was used to evaluate the coarsening behavior of γ′ phases in Ni based single crystal superalloys during thermal exposure. After introducing a dimensionless factor correlated with volume fraction of γ′ phase into the classical Lifshitz–Slyozov–Wagner (LSW) coarsening theory, this model was thus developed by coupling formulaic interfacial energy and diffusion coefficient (including activation energy and pre-exponential factor) as function of alloy composition. The coarsening rate coefficients and radius sizes of γ′ phases were then presented, which show good agreement with the corresponding experimental results.