Among various methods for calculation of the plastic strain ratio (γ value) of deep drawing steel sheet, the crystallographic approach is rather preferred because it is founded on the slip action during the crystal plastic deformation, while the crystal deformation mechanisms are fully taken into account. Thus it possesses a more soundly theoretical basis. However, its two assumptions, i.e. the same critical shear stresses for the three different slip systems in BCC and no orientation changes for all crystallites in tensile test samples in elongation up to 15％, are inconsistent with the experimental evidence. Among various methods for calculating the plastic strain ratio (γ value) of deep drawing steel sheet, the crystallographic approach is rather preferred because it is founded on the slip action mechanisms are fully taken into into account However, its two assumptions, ie the same critical shear stresses for the three different slip systems in BCC and no orientation changes for all crystallites in tensile test samples in elongation up to 15%, are inconsistent with the experimental evidence.