Observations of the magnetic domain structure using a colloid method of strained grain oriented 3% SiFe alloy are reported. Density of the supplementary structure rises dramatically with small increases (about 2%) in plastic deformation. Transverse domain patterns suddenly appear around 4-5% of plastic strain. Close to the rupture of the alloy, zigzag lines and dissociation of main domain walls are observed. A statistical analysis of the different magnetic domain patterns has been made. An evolution in three distinct linear stages of the superficial densities of main and secondary structures is shown. Domain wall spacing of the main structure markedly decreases between 0 and 3% of strains and monotonous fall of domain wall spacing of the transverse patterns occurs. These experimental results establish that the transverse domain structure allows a compensation of the increase of the magnetoelastic energy that results from cold drawing of the alloy.