Distributed sensing for gearbox operation and anomaly detection is essential to improve gearbox design and fault detection to reduce the operation and maintenance cost for wind energy. In this study, we demonstrate the feasibility of real-time distributed strain monitoring of gearbox operation using Distributed Fiber Optic Sensing (DFOS) with Optical Frequency Domain Reflectometry (OFDR). Leveraging the millimeter scale spatial resolution and high strain accuracy of DFOS, we performed an experimental test involving a gearbox with multiple planetary gears under varying load conditions. In this test, a single optical fiber was attached to the outer surface of the gearbox continuously, providing a comprehensive strain profile as the inside gears rotated. The operation status of the gearbox, including the locations of the planet gears can be clearly observed in real-time, and the rotation speed can also be calculated based on the measurements. The results also revealed a linear relationship between the load torque and the strain measurements at all locations, underlining DFOS’s capability to accurately quantify torque load and detect potential faults at an early stage.