The accurate estimation of reaeration rate coefficient, because of its effects on dissolved oxygen in rivers, is one of the most important initial steps of water quality management. The main goal of this paper is to evaluate the effects of reaeration rate coefficient on the river water dissolved oxygen, case study Dinachal River, Iran. To achieve these aims, water quality samples were collected along a reach of 2 kilometers of the river in September 2013. Electrical Conductivity, pH, Dissolve Oxygen, Biochemical Oxygen Demand, Nitrate and Phosphorus are the main quality parameters which were measured in laboratory, using the above mentioned collected water samples. Streeter-Pheps model has been used to simulate dissolved oxygen in the river analytically and to improve the output of the model advection, dispersion and decay rate terms were included to the basic form of the Streeter-Phepls equation. In addition, dissolved oxygen concentration in the river has been simulated involving FTCS, QUICKEST, Upstream and Lax-Wendroff numerical methods. The reaeration coefficient has been estimated using four eempirical equations including; Oconnor-Dobbins, Langbein-Durum, Boulton and Ling et al.. The results show that Up-stream numerical method containing Boulton rreaeration Coefficient equation has the most accurate results, with the amounts of Pearson correlation coefficient and Mean Absulate Errors equal to 0.995 and 0.033, respectively.