Abstract: Affected by complex temperature boundaries and operating environments, the internal temperature distribution and long-term stress status of high concrete gravity dams in Southwest China are difficult to obtain directly. Taking Monolith 17 of the Jinghong Gravity Dam as the research object, a two-dimensional finite element model of the dam?foundation system is established based on monitored temperature data, reservoir water level records and plumb line displacements. The temperature boundary conditions on the upstream and downstream dam surfaces are fitted, and the operating temperature field is calculated and validated using monitored internal temperatures. Meanwhile, the elastic modulus of dam concrete is inversely calibrated using the measured displacement data. On this basis, the stress distribution during operation is numerically simulated. The results show that the reservoir water temperature in front of the dam exhibits obvious stratification along the elevation; the upstream face temperature is mainly controlled by the reservoir water, and the internal temperature field of the dam is generally stable. The horizontal displacement of the monolith in the upstream-downstream direction agrees well with the variation in air temperature but shows no obvious correlation with the reservoir water level. The dam is mostly under compression, while small tensile stress zones appear locally on the upstream face above the water level under low-temperature conditions. It is indicated that Monolith 17 is in a stable working state during operation, and thermal action is a key factor affecting the deformation and local stress distribution of the monolith.