A hydrogen sensor based on a cross spiral-micro-structured fiber Bragg grating (FBG) is developed. We employ a femtosecond laser to fabricate the cross spiral microstructure on the fiber cladding and then coat the surface of the FBG with a Pt-WO₃ film prepared by a hydrothermal method. The hydrogen sensitivity of the spiral micro-structured probe is 1.55 times higher than that of a non-micro-structured FBG hydrogen sensor. We determine the sensitivity of the sensor from numerical simulations and discuss the difference between the simulation values and the experimental results. The sensor has the characteristics of high sensitivity, fast response, and good repeatability, and it has significant application prospect for monitoring hydrogen leakage.