Abstract: The scanning compensation system is a key part of 3DLIF water measurement system to realize optical path scanning such as large-size planar laser, which determines positioning accuracy of planar laser beam in the fluid sink.This 3DLIF water measurement system has a long optical path length of 3 000 mm and a 500 mm wide light source, which makes it difficult to guarantee positioning accuracy.In order to solve this problem, influence factors of error factors and various factors in scanning compensation system are analyzed.Relevant error model is established and simulation analysis is carried out.The obtained error data are fitted by polynomial fitting and fitting result shows the angle between prism manufacturing and pitch of plane mirror around z axis are main factors that affect position error.In order to reduce the error, fitting result is further analyzed, and the relationship expression between two factors is obtained.Final simulation results show that position error of planar laser in the sink can be reduced from 0.618 mm to 0.103 mm by this method.