When a helicopter rotor blade rotates at high speed, the measurement and analysis of blade lead-lag motion in the full field are of great significance for the load design of helicopter blades and rotor structure design. In this article, a stereo vision measurement system for blade lead-lag motion is designed, and the lead-lag motion mode fitting analysis is carried out. First, the existing stereo vision measurement system of the subject group is improved, and the 3D coordinates of the rotating blade marker points at different collective pitch and cyclic pitch are measured in wind tunnel tests. Secondly, the blade lead-lag motion in the hub coordinate system is calculated. Finally, the first order polynomial is used to fit the blade lead-lag motion pattern at a specific moment, and the compound sine function is used to fit the blade lead-lag motion law during rotation. Experimental results of wind tunnel measurements show that the root mean square error of the measured lead-lag motion in the 4. 6 m×4. 6 m scenario is less than 1 mm. Blade lead-lag motion modes and law models fit well, with root mean square error less than 1 mm, providing data support for helicopter blade design.