In order to study the microstructure control of continuous casting slab of grain oriented silicon steel, the method of field trial was adopted to analyze the influence of different factors on the microstructure of slabs by adjusting the process parameters that affect the formation and transformation of equiaxed crystals and columnar crystals. Studies have shown that as the superheat increases, the proportion of equiaxed crystals in the grain oriented silicon steel slab decreases. The use of electromagnetic stirring can achieve the casting of grain oriented silicon steel under the condition of the superheat exceeds 40°C and the proportion of equiaxed crystals >50%. The box-type of electromagnetic stirring in secondary cooling zone can be used to effectively control the proportion of equiaxed crystals of the slab from 10% to 75%, and increase the electromagnetic stirring current, which contribute to the linear increasing of the proportion of equiaxed crystals. The increasing of the casting speed and width range is conducive to the proportion of equiaxed crystals in slabs. Meanwhile, moderate electromagnetic stirring intensity (400 A, 3 HZ) is beneficial to the uniformity of the slab composition with the optimal effect of improving the segregation along the thickness direction of the slab. The deviation of the measured and predicted value of the equiaxed crystal proportion of the slab is less, the effective control of the equiaxed crystal ratio can be achieved by adjusting the process parameters.