As a potential energy carrier and industrial material, the increasing importance of hydrogen calls for trace gas detection technique with higher sensitivity, faster response and wider dynamic measurement range. Based on the Pound-Drever-Hall (PDH) laser frequency stabilization technique, laser is coupled into a high-finesse optical resonant cavity in cavity-enhanced Raman spectroscopy (CERS) system, resulting in a power gain factor of 1900 for trace hydrogen gas sensing. With 7 mW input laser power and 100 s exposure time, a detection limit of 2 Pa for hydrogen gas is achieved for the home-made CERS system. Measurements also show that the signal of Raman scattering has an excellent linear relationship with the gas pressure and laser power, which indicatesCERS has the potential for quantitative analysis of gases with high precision.