In order to implement the seepage monitoring with temperature in embankment dam with the popular distributed fiber optic temperature sensor system (DTS), it’s necessary to study the background characteristics of temperature field. Herein, a saturated-unsaturated seepage field and temperature field coupling model (thermal-hydro coupling, i.e. T-H) is established. The model considers the heat convection-conduction-diffusion, as well as the boundary periodically fluctuation with atmosphere temperature. Some parameters are considered nonlinearly so that the result of simulation is closer to the true state of dam temperature field. For instance, the fluid viscosity is influenced by temperature and thermal conductivity is influenced by moisture, and so on. A clay core embankment dam is taken as a case study. It is shown that the temperature field within the dam has the characteristics of seasonal fluctuation, which is controlled by seepage and atmospheric temperature. Specifically, the heat from the reservoir controls the temperature variation of the saturated zone and the heat from atmosphere controls that of the unsaturated zone. If the core wall leaks, the temperature nearby will reduce as cold reservoir water flowing into. In this case, the distributed fiber sensors lying on the core wall can be used to detect spatial and temporal distributions of leakage. The conclusions are drawn as follows that the seepage monitoring with temperature is effective in theory. In the data analysis, particular attention should be paid to the temperature anomalies caused by atmosphere temperature.