Abstarct: Today,the existence of water and wastewater treatment plants are of special importance in order to provide better health conditions for people's lives, keep the environment clean and recover sewage. The use of diagonal plates in order to increase the flow length in a pond increases the possibility of improving the efficiency of the sedimentation pond. In this study, the influence of the hydraulic properties of the flow (flow rate (0.016, 0.032, and 0.096 cubic meters per hour) and residence time (0.5, 1.5, and 3 hours)) and the geometric properties of diagonal plates (including number (without diagonal plate), 1, 2 and 3 diagonal planes) and placement angle (45, 50 and 60 degrees)) on the efficiency of chemical oxygen treatment of wastewater (COD), removal of turbidity, removal of suspended particles (TSS) and removal of color of wastewater treatment plant of yeast production factory has been investigated The results showed that by reducing surface loading and solids loading (resulting from the decrease in flow rate (increasing residence time)), increasing the effective surface of diagonal plates and the optimal combination of two factors, the number and placement angle of diagonal plates, the efficiency of the sedimentation basin increased significantly. Finds. In general, the highest COD purification efficiency, removal of TSS, turbidity, and color in the sedimentation pond is related to the residence time of 3 hours and in the case where 3 diagonal plates are installed in the pond at an angle of 45 degrees. The removal and purification efficiency of COD, TSS, turbidity, and color in the best conditions of placement of diagonal plates and retention time were 1.46, 2.02, 0.99 and 0.58%, respectively, compared to the case where the pond did not have diagonal plates, increased. Also, the amount of surface load and solids load of diagonal plates in the most suitable position of placing the plates in the basin and the dwell time has decreased by 21.75% compared to the case where the basin had no plates, These changes have increased the efficiency of the sedimentation pond. The results of the sensitivity analysis also showed that the retention time has the greatest effect on the efficiency of the sedimentation pond, and then the changes in the number and angle of the diagonal plates have the same relative effects on the efficiency of the sedimentation pond.