To study the application of laser Raman spectroscopy to analysis fusion fuel processing gas, six hydrogen isotopes were experimentally measured. Raman spectra of these mixture gases showed that the useful lines for quantitative analysis are Stokes rotations below 1000 cm−1, with representative lines for H2, HD, D2, HT, DT and T2 being 587, 443, 415, 395, 250 and 200 cm−1 respectively. The absolute Raman intensity ratio was estimated as H2:HD:D2:HT:DT:T2 = 100:58:47:46:36:41. With the laser wavelength of 488 nm, power of 700 mW and using a multiple pass system, the detection limit for H2 was 10 Pa, which was the equivalent of 100 ppm in concentration. As a remote sensing technology, the optical fiber was verified as applicable for transferring the irradiation laser beam.