After coarse calibration of the binocular 3D vision system, there still are large systematic errors existed. In order to
improve the measurement accuracy, we directly calibrate the existed systematic errors after simple calibration steps of
the binocular vision system. The depths of the targets located at different distances are measured at three different field
of views(FOVs). After got original results, the relationship between the depth errors, the field of views and the distances
is analyzed. The error curves for correction are obtained. The largest error is about 26% and after the correction the error
is below 5%. Also a simple matching program is designed to automatically match the feature points at left and right
images, and to calculate the depth of the feature points.