In order to describe the dislocation cell structure formation process in the light of collective dislocation behavior, the reactions of dislocations such as multiplication, mobilization, immobilization and dynamic recovery are indispensable. In this study, we employ Reaction-Diffusion equation for time evolution equation of dislocation densities. This paper aims to reveal the cell formation process in terms of microscopic variable (dislocation density distribution) and macroscopic variable (effective stress). We also perform stability analysis on simultaneous Reaction-Diffusion equations and critical wave length which characterizes the dislocation cell structure is obtained as a function of effective stress.