Cement rotary kilns are extensively used to change raw material into clinker. This is a complex process and consists of many different phenomena such as bed material reactions, gas phase turbulent combustion and radiation in a rotary drum, and thermal-mass interactions between them. Using CFD, the two-dimensional numerical simulation of cement rotary kiln was performed in the present study. This model included gaseous fuel combustion, bed material reactions, and radiation heat transfer in the kiln. Using this model and parallel processing network, combustion models (PaSR, EDM and mixture fraction) in the cement kilns are investigated. Due to the high Damkohler number in the cement kiln (0.7<Da<17), selecting the appropriate combustion model is difficult. Among the combustion models that were studied, it was found that the PaSR model is the slowest and mixture fraction model is the fastest model whereas the both models predict physics well. Keywords