The work aims to optimize the tensile stress of the coating, so as to improve the magnetic properties of grain-oriented silicon steel. The thickness and microstructure of colloidal silica insulation coating with phosphate were analyzed by SEM and GDS and the mechanical properties of substrate along different direction were acquired by tensile test. Based on the anisotropy of grain-oriented silicon steel and the real state of coating, the applicability of Stoney equation to the grain-oriented silicon steel coating was discussed. The anisotropy of grain-oriented silicon steel did not meet the applicable conditions of Stoney equation and the mechanical properties of grain-oriented silicon steel tested in practice showed that the grain-oriented silicon steel conformed to the general law of orthotropic material. Based on that, the equation was given to calculate the tensile stress induced in the substrate of oriented silicon steel by the colloidal silica insulation coating under different technology parameters. The tensile stress was 4~11 MPa when the coating thickness was within 1~2 microns. The equation for calculating the tensile stress is not only applicable to grain-oriented silicon steel, but also applicable to similar cases where other substrates are anisotropic. Through calculation of tensile stress, the stress and thickness of the insulation coating have a positive correlation and the iron loss reduce with increasing of the stress induced in substrate by the coating. Therefore, the research and development of insulation coating with higher tensile stress is the effective method to improve the magnetic properties of grain-oriented silicon steel.