As one of the most important components participating in the pumping reaction of CW DF/HF chemical laser, the distribution of fluorine-atom has direct influence on pumping and lasing especially for the cold-reaction operation. Because of free-stream recombination and wall-catalytic recombination, some of the fluorine atoms will be recombined with molecules before entering into the reaction region. It's very important to investigate fluorine-atom' distribution for the analysis and optimization of lasers. Some experimental methods have been developed and theoretical model has been established. The model and general computational fluid dynamics (CFD) tool were combined to compute the fluorine atom distribution. Its validity was tested, and cases under different converge contour were numerically studied.