In the present study, the increase in the accuracy of numerical simulation of two-phase combustion in the combustion chamber of a ducted rocket engine has been investigated. The present problem includes two fuel flows with gas and solid phases. For the numerical simulation of two-phase combustion in a ducted rocket engine, ANSYS Fluent software has been used. For the modeling of turbulence, the two-equation model of k-ε RNG has been intended. Also, for the modeling of combustion and solid carbon particles, the non-premixed combustion model and the DPM model have been used, respectively. Using an unorganized grid cell, examining the sensitivity of the numerical solution results to the number of grid cells, the value of the flammability limit of the solid fuel flow, and using the turbulent dispersion model and its sub-parts in discrete phase modeling are the applied differences in the present CFD research. In fact, the use of the turbulent dispersion model and its sub-parts has had a major impact on improving the numerical simulations performed. The difference between the two-phase combustion efficiencies obtained from CFD in the present work and the two-phase combustion efficiencies obtained from the experimental work in configurations 1, 2, 3, 4, and 5 has decreased by 22%, 6%, 0.4%, 4% and 5%, respectively, which means an increase in the accuracy of the numerical simulation of two-phase combustion in the present work.