A study concerns the dispersion of pollutants in Diyala River using one-dimensional Finite ditference technique (implicit method) to solve the simplified dispersion equation. The model starts at Diyala barrage and extended to the confluence of the Tigris Diyala rivers, and for 203-Km length. The simplified dispersion model results were verified by comparison with the analytical solution for different time increments. The calibration of the model was conducted on 31/11/1998 using measured data (discharge, velocity, cross sectional area, total dissolved solids (TDS), chloride CL and sulfate (SO)) concentrations at the same day and the results indicated a good agreement between the computed and measured data. The verification of the model is accomplished on 13/12/98.27/12/98.10/1/99,25/1/99) and the results indicates also the accuracy of the applied model simulate the conservative salts (TDS. CL. So) in the river.