Abstract: The influence of cold working deformation on dislocation density of IF steel was studied.After the cold working deformation, there were amount of dislocations in IF steel.The dislocation density of IF steel increased with the increment of deformation extent.With the deformation up to 20%, the fibrous structure appeared in the crystal of IF steel, and became sub-grains.The relationship between dislocation density (ρ) and deformation amount (A) could be shown as the formula:ρ=2.205 17×1014+1.049 5×1016A.