In electronic speckle shearing test systems, the shear has a big impact on measurement accuracy, sensitivity, and the fringe contrast. This article introduces the principle of electronic speckle shearing interferometry and the relationship among shear and measuring accuracy, sensitivity, and the fringe contrast map. And MATLAB is used to simulate the electronic shearography speckle pattern under different amount of shearing and generate a lot of valid images. The method for selecting shear is proposed through the combination of theoretical analysis and simulation. Tire deformation detection experiment achieves good results by using the method and verifies the effectiveness of the method. The research work on this article plays a practical guiding role on selection of shear in non-destructive detection system.