A novel, to the best of our knowledge, mirror-assisted binocular stereo digital image correlation (DIC) system is proposed for the reconstruction of the overall contour, thickness, and strain measurement of the object. First, the angle between the two plane mirrors is adjusted until two virtual images and two real images can be formed in the mirrors. Then, the adjustable speckle size and definition characteristics of the projection speckle technology are fully utilized to realize the precise measurement of the mirror plane. Finally, a 3D contour reconstruction experiment and a dynamic stretching experiment are conducted to verify the proposed method. Experimental results show that the proposed method can achieve a 360° omnidirectional deformation measurement, and the 3D reconstruction of the object with complex contours has a relatively ideal reconstruction effect. According to the virtual image, the thickness of the conventional specimen can be completed easily, and the coordinates of the front and rear surfaces need not be subtracted. The dynamic strain can be calculated separately from the front and rear surfaces of the standard specimen and can be realized in the dynamic tensile experiment. Compared with the existing binocular DIC system, the proposed method can provide more valid data with guaranteed excellent results. It provides a better implementation method for omnidirectional measurement, thickness, and stress-strain calculation of the object.