High-power fiber-to-fiber coupling is extensively used in fiber laser applications, and its performance is determined by coupling efficiency. We demonstrate a novel method for alignment and monitoring efficiency by detecting backscattering power at the fiber end cap. The relationship between alignment error and backscattering power is determined by simulations and experiments. Through this method, a state-of-the-art kW-level fiber-to-fiber optic switch is developed (transmission efficiency >97%). It performs well for longer than 60 min. To the best of our knowledge, it is the first time to establish the mathematical model based on this method. Our results can provide guidance in high-power fiber-to-fiber coupling.