A low-interference non-contact torque measuring system is designed for real-time measurement of torque on transmission shaft helicopter. This system is based on the timing principle

and utilizes fiber after which the torque value is calculated according to the relationship between torque and torsion angle. To improve the precision and the operating distance

collimation structure of fiber sensor is designed

and the spot diameter is decreased. Bilateral timing is utilized to eliminate the error caused by common-mode interferences

and encoding strip error influence is eliminated. Experiments are carried out on ground testing platform. Experimental results demonstrate that the systemic resolution can reach to 0. 0002°. the repeatability precision is 0. 005°

and lowinterference non-contact torque measurement for helicopter shaft is realized.