A high-precision measurement method based on laser collimation and photoelectric detection is proposed to address the challenge of dynamically measuring the deflection angle of helicopter transmission shaft systems under highspeed operation. A collimated laser beam serves as the measurement datum. Spot coordinates of the laser beam are acquired by photoelectric detection modules to determine the relative position and attitude of the probes. During high-speed rotation of the transmission shaft system

multiple probes are arranged to synchronously measure several cross-sections of the shaft. The shaft center trajectory of each cross-section is obtained using a three-point error separation algorithm. Based on this

the dynamic deflection angle between two shaft segments is fitted and calculated. Experiments were conducted under different initial installation angles and rotational speeds. Results show that the synchronization accuracy of the probes is better than 100 ns

the measurement frequency of the deflection angle exceeds 2000 Hz

and the measurement uncertainty is better than 10″. The system meets the requirements for dynamic deflection angle measurement in helicopter transmission shaft systems.