A numerical simulation for the carbonization step during processing of two dimensional (2-D) carbon/carbon (C/C) composites was studied. The composites were made of phenolic resin and carbon fabric. Two-stage decompositions of phenolic resin were used. Subsequently, a 2-D finite difference method (FDM) was used to solve the governing equations for the flow of gases during carbonization in C/C composites. For solving the problem, the combined effects for degradation of phenolic matrix and increasing temperature during carbonization on the material properties were studied. Using material properties, numerical simulation provides pressure, temperature, porosity distribution, specific heat, thermal conductivity, density and viscosity of evolved gas as a function of processing time/temperature and space. The results of 2-D numerical simulation code were compared with the results of a previously published one-dimensional FDM.