The invention provides a heat flux coupling simulation building method for a dam downstream riparian zone based on Lu model. The method includes the steps that 1, a riparian saturated-unsaturated seepage field-temperature field full coupling model is built, the model building includes the establishment of a seepage field, the building of a saturated-unsaturated heat migration model, and the description of the relationship between a temperature field and a seepage field; 2, boundary conditions are set for the riparian saturated-unsaturated seepage field-temperature field full coupling model, the setting of the boundary conditions include the setting of boundary conditions for the seepage field and the setting of boundary conditions for the temperature field; 3, the riparian saturated-unsaturated seepage field-temperature field full coupling model is solved, the Lu model is used to describe the relationship between equivalent heat conduction coefficient and water content of soil body inthe solving process, and the variation rule of temperature with time is obtained in the seepage process. The problem that an influence mechanism of dam discharge low temperature water to the saturated-unsaturated heat flux coupling in the dam downstream riparian zone cannot be simulated accurately in the prior art is solved.