Tungsten oxide (WO3) typically owns the characteristics of electrochemical, photo-chromic, and gas-chromic. The seven-core fiber (SCF) generates a strong interference signal that comprises super-modes. The thermo-optic and thermo-expansion characteristics of SCF were utilized with an aid of Pt-WO3 film that makes the sensor highly sensitive to the H2 gas environment. The sensor with spiral micro grooves by femtosecond-laser ablation considerably enhanced the H2 sensitivity from 3.28 nm% to 4.0 nm%, and obtained a response and recovery time < 90 s.