The Area-Reduction method is one of the experimental methods to estimate sediment distribution in dam reservoirs. In this method, the reservoirs classify based on the geometry into four types. Then the sediment distribution in each type of reservoir specify based on the related parameters. Results of previous researches were shown that in most of the cases; determining the type of reservoir with the Borland and Miller method didn’t lead to an accurate estimation. So, determining the optimized coefficient for the Area-Reduction method can increase the accuracy of sediment distribution prediction in this method. In this study, initially a computer model was provided based on the Area-Reduction method by using MATLAB software, then the optimization model was prepared based on the Ant Colony algorithm and these two models were combined. Best coefficients of the Area-Reduction method for Karaj Dam were obtained from developed model. The results showed that there was a significant increase in accuracy of predicting the sediment distribution using optimal parameters. Using the optimal parameters decreased the error values up to 68.41%.