The concrete core walls with steel plate bracings are simulated by finite element software ABAQUS, and the simulated results are in good agreement with the test results. The effects of loading process，aspect ratio, coupling beam steel ratio，corner column steel ratio，concealed column steel ratio and concealed bracing steel ratio for the shear lag are discussed, and the minimum effective flange width for various conditions is obtained. The results show that the effective flange width be reaches the minimum value when the core wall yields. The shear lag effect weakens as long as the aspect ratio increases, and thus the value of be increases. The reinforcement ratio and steel ratio have little impact on be，but be increases with the effect of span-depth ratio of the coupling beam. The axial load ratio is also helpful for the growth of be. Increasing the steel ratio of the corner column and concealed bracing increases be，but the effect of the concealed column steel ratio is not significant.