The vigorous internal-tide-induced mixing in the Indonesian seas, which provide the only low-latitude passage of thermohaline exchange between the Pacific and Indian Oceans, makes significant effects of the Indo-Pacific regional and even global hydrodynamical environment and climatic system. A western Pacific and northern Indian regional Oceans Model (PIOM) simulation with nine primary tidal constituents (M₂, S₂, K₁, O₁ et al.) is used to simulate the ocean circulation and thermohaline environment form 1990 through 2020 in the Indonesian seas. The baroclinic energy budget analysis reveals that the high internal-tide-induced dissipation occurs in the entrances (Sulawesi Sea and Halmahera Sea) and the exits (Lombok Strait and Banda Sea) of the Indonesian Throughflow (ITF) with the estimated depth-integrated dissipation rate exceeding O(10^-1) Wm^-2. It shows a clear fortnightly spring-neap amplitude in tidal mixing energy dissipation in the areas where internal tides generate, which is stronger in the seasons of summer and winter, while weaker in spring and autumn. The seasonal variation of the spring-neap swing in tidal mixing energy dissipation is dominated by the stratification condition especially the perturbation of density in the exits of ITF, but is affected by the co-operation for regional thermohaline environment and local circulation in the entrances of ITF.