The inhomogeneity of temperature in a turbine is related to the nonuniform heat release and air injections in combustors, which is commonly measured by thermal couples at the turbine exit. Investigation of temperature inhomogeneity transportation in a multistage gas turbine should help in detecting and quantifying the over-temperature or flameout of combustors using turbine exhaust temperature. Here, the transportation of combustion inhomogeneity inside the four-stage turbine of a 300-MW gas turbine engine was numerically investigated. The computational domain included four turbine stages, consisting of more than 500 blades and vanes. Realistic components (N2, O2, CO2, and H2O) with variable heat capacities were considered for hot gas and cooling air. Coolants were added to the computational domain through more than 19,000 mass and momentum source terms. An unsteady Reynolds averaged Navier–Stokes computational fluid dynamics (URANS CFD) run with over-temperature/flameout at 6 selected combustors out of 24 was carried out. The temperature distributions at rotor–stator interfaces and the turbine outlet were quantified and characterized using Fourier transformations in the space domain. It is found that the transport process from the hot streaks/cold streaks at the inlet to the outlet is relatively stable. The cold and hot fluid is redistributed in time and space due to the stator and rotor blades, and in the region with a large parameter gradient at the inlet, a strong unsteady temperature field and a composition field appear. The distribution of the exhaust-gas composition has a stronger correlation with the inlet temperature distribution and is less susceptible to interactions.