A three-dimensional (3-D) digital image correlation system for deformation measurement in experimental mechanics has been developed. The key technologies applied in the system are discussed in detail, including stereo camera calibration, digital image correlation, 3-D reconstruction, and 3-D displacement/strain computation. A stereo camera self-calibration algorithm based on photogrammetry is proposed. In the algorithm, the interior and exterior orientation parameters of stereo cameras and the 3-D coordinates of calibration target points are estimated together, using the bundle adjustment technique, so the 3-D coordinates of calibration target points are not needed in advance to get a reliable camera calibration result. An efficient image correlation scheme with high precision is developed using the iterative least-squares nonlinear optimization algorithm, and a method based on a seed point is proposed to provide a reliable initial value for the nonlinear optimization. After the 3-D coordinates of the object points are calculated using the triangulation method, the 3-D displacement/strain field could then be obtained from them. After calibration, the system accuracy for static profile, displacement, and strain measurement is evaluated through a series of experiments. The experiment results confirm that the proposed system is accurate and reliable for deformation measurement in experimental mechanics.