In most streams, pollutants are mixed vertically before mixed transversely because depths of the streams are typically smaller than widths. Thus, in this model, 2-D depth-averaged advection-dispersion equation of water temperature was formulated by finite element model. RAMS-GUI and RAM2 are adopted for water temperature model. Using RAMS-GUI which is the computing module of software RAMS, the finite element mesh of application site was generated. Developed water temperature model using FE method is verified in rectangular channel by 1-dimensional analytical solution. The developed model in the real problem was applied in Han River from Paldang-dam to Jamsil bridge.