On the background of the image of online detection of rail transport wheel-set parameters, a kind of high accurate synchronization flash image acquisition method was proposed in order to solve the problem of short exposure time and lack of exposure when the vehicle wheel-set moving fast. The exposure and flash time sequence was designed in synchronous timing, using high-intensity flash light to ensure luminous flux. Trigger signal was processed by optical coupler and MCU. And with high-precision delay control module, the exposure and flash moments could be controlled. Asynchronous image acquisition was designed and realized so that a clear image can be acquired accurately when the wheel-set arrives at the position set in advance. The influencing factors of the synchronization error were analyzed. According to the results of experiment, when the speed is less than 80 km/h, the synchronization error of the system would be less than 25 μs and the motion blurred would be less than 1 mm.