Strain results obtained using common two-dimensional digital image correlation (2D-DIC) method usually have rather poor measurement accuracy owing to rigid out-of-plane displacement. This study proposes a modified 2D-DIC method based on 45° dual-reflector imaging technique to improve the strain measurement accuracy. The speckle patterns of the front and rear surfaces can be recorded in a single image using dual-reflector imaging. The effect of rigid out-of-plane displacement is automatically eliminated by taking the average strain of corresponding points from the left and right images. Two groups of tensile tests are conducted to verify the feasibility of the proposed 2D-DIC method. Experimental results show that: for uniform deformation, the biaxial results obtained using the proposed 2D-DIC method are in good agreement with those obtained using strain gauges; from the viewpoint of the nonuniform deformation, the strain fields of the proposed 2D-DIC method are in agreement with those of the finite element method. Therefore, the proposed 2D-DIC method has excellent strain measurement accuracy, and it is a convenient, effective, and highly accurate strain measurement method.