For monitoring the sloshing of the rocket body for liquid launch vehicle on long-term duty, and ensuring the safety and stability of the product, an on-line monitoring method of rocket body sloshing based on binocular vision measurement was proposed. Firstly, the internal and external parameters of the camera were calibrated with high precision by total station and other devices. Secondly, the precise coordinates of the same marked point at different time were measured. Finally, a set of equations were constructed to solve the parameters of pose transformation through the coordinate changes of the marked points at different times and the constraint conditions, and then the amount of rocket body sloshing was obtained. The results show that the maximum measurement error and total deviation of single marked point are 0.026 mm and 0.079 mm respectively, which can effectively meet the actual needs of on-line monitoring of rocket body sloshing.