Taking an Inconel 718 (GH4169) turbine disk with an accumulated service time of approximately 60,000 hours from a specific model of aircraft as the research object, this study systematically investigates the microstructure of various regions of the service turbine disk. Detailed characterization of the microstructure was conducted using research methods such as optical microscopy, scanning electron microscopy, electron probe, extraction phase analysis, inclusion scanner, and nano-indentation. The results show that after long-term service, there is no significant change in the strengthening phases γ" and γ" of the turbine disk. However, the quantity, size, and morphology of primary MC carbides from the center to the edge have undergone noticeable decomposition. The content decreased from 0.166 wt.% to 0.106 wt.%, and the morphology gradually changed from sharp and regular blocky shapes at the interface to irregular near-circular shapes. The nano-hardness decreased, and there was a significant redistribution of elements, with Nb, Ti, and C elements released and diffused into the matrix. The primary MC carbides are prone to dissolution and decomposition during long-term service, leading to a decrease in the concentration and hardness of the carbide elements. The diffusion of carbide-forming elements into the matrix may cause a "disturbance" to the comprehensive mechanical properties of the alloy during the long-term service performance.