This paper mainly proposes an online interference measurement approach of the film thickness in sliderondisc conformal contact. With a monochromatic laser, the physical characteristic of the parallel straight interference fringes translation induces by variation of the film thickness. Based on optical flow calculation and dynamic time wrapping technique, a hybrid algorithm is introduced to calculate the displacement of an onedimensional intensity curve across the parallel fringes between two adjacent frames, therefore, the corresponding film thickness change can be obtained. From the start of the test rig, the film thickness variation of each frame is recorded and the online film thickness measurement is achieved. The film thickness by the presented approach is validated by its good correlation with that by the old offline method. With the new measurement system, the transient film thickness is measured in real time under conditions of step loads, uniform acceleration and deceleration, and some characteristics of film building are demonstrated.