Aiming at the problem that the traditional plunged-bar method is difficult to meet the measurement requirement of spatial location of thin and small through-hole, in this paper, the digital image processing technique combined with sub-pixel detection technique is employed, and a new method is proposed to detect the tiny through-holes. The evaluating function method based on the “roundness” of the image of hole is presented to find out the posture parameters of CCD where the optical axis of CCD is parallel to the centerline of hole. Therefore, the spatial location of hole can be easily obtained by these posture parameters. Meanwhile, the diameter of hole can be achieved by means of image measuring technology at calculated posture of CCD. Owing to the non-contact measurement, this method is particularly suitable for those small through-holes drilled on the soft and easy-deformed object. The experiment results on the experimental platform illustrate the feasibility and validity of this method.