The ‘Helmholtz movement’ of a bowed string was analyzed, and a non-contact optical measurement system based on high-speed photography was designed to measure the vibration of string of a violin. By designing a special path and setting a marked point on the string, the three dimensional vibration state of the marked point on string was measured on plucking and bowing the violin string with a high speed shooting rate of 7 000 frame/s and image resolution of 336×480. On the imaging processing algorithm based on the circular Hough transform, singular value decomposition algorithm and an automatic batch program, a large number of sequential images recorded were processed and the displacement and trajectory were extracted. The experimental results show that the proposed measurement system accurately tracks the motion and trajectory of the violin string, and the data processing accuracy of vibration displacement is 0.03 mm. The designed measurement system and image processing algorithm provide a valid experimental method for studying the mechanism of violin string vibration and developing an accurate theoretical model for string motion.