In order to quickly detect hydrogen leaks, there is an urgent need to develop a safer and lower concentration detection lower limit hydrogen sensor. This article assembles a micro cantilever beam probe coated with palladium film with a single-mode fiber end face, and designs an easy to prepare and low-cost fiber optic hydrogen sensor. The experimental results show that the sensor has an ultra-high hydrogen response sensitivity of about -9.887 μm/%, while also having an ultra-low detection lower limit as low as 1.76×10^-3% and excellent repeatability. Under the conditions of trace hydrogen volume fraction, the sensor exhibits excellent linear response to hydrogen volume fraction, which is of great significance for trace gas detection and has important application value in hydrogen energy batteries, nuclear power plants, and space exploration.