Assuming that decomposition of organic matter in soils follows the first-order kinetics reaction, a computer model was developed to simulate soil organic matter dynamics. Organic matter in soils is divided up into two parts that include incorporated organic carbon from crop residues or other organic fertilizer and soil intrinsic carbon. The incorporated organic carbon was assumed to consist of two components, labile-C and resistant-C. The model was represented by a differential equation of dCt/dt = Kt × fr × fw × fs × ct (i = 1, r,S) and an integral equation of Cit = Cio × EXP(Ki × fT × fw × fs × t). Effect of soil parameters of temperature, moisture and texture on the decomposition was functioned by the fT, fw and fs, respectively. Data from laboratory incubation experiments were used to determine the first-order decay rate K, and the fraction of labile-C of crop residues by employing a nonlinear method. The values of K for the components of labile-C and resistant-C and the soil intrinsic carb Assuming that decomposition of organic matter in soils follows the first-order kinetics reaction, a computer model was developed to simulate soil organic matter dynamics. Organic matter in divided into two parts that include incorporated organic carbon from crop residues or other organic fertilizer and soil intrinsic carbon. The incorporated organic carbon was assumed to consist of two components, labile-C and resistant-C. The model was represented by a differential equation of dCt / dt = Kt × fr × fw × fs × ct (i = 1, r, S) and an integral equation of Cit = Cio × EXP (Ki × fT × fw × fs × t). Effect of soil parameters of temperature, moisture and texture on the decomposition was functioned by the fT, fw and fs , respectively. Data from laboratory experiments experiments were used to determine the first-order decay rate K, and the fraction of labile-C of crop residues by employing a nonlinear method. The values ​​of K for the components of labile-C and resistant- C and the s oil intrinsic carb