A measuring system based on optical coherence tomography was established to measure the distance of optical surfaces non-contactly. The system was developed by modifying the sample scanning device based on a time-domain optical coherence tomographic system. The tomographic images of optical surfaces in different depths were acquired by moving the fiber collimator in sample arm through a high precision guide. The distance of an air gap sample and a lens were measured by using this system. Results show that the measured value of air gap sample is 6.026 mm while it is 6.02 mm by using a vernier caliper. Furthermore, the measured value of air gap in the lens is 10.750 mm while its design value is (10.7±0.03) mm.The systematic error is 3.871 μm and the sensitivity is 10.5 μm. The measurement method is characterized by non-contact, high precision, and high sensitivity, and has great potential in optical material testing.