Continuous observation of hydrogen concentration in fault belt is an important gas geochemical index on deep tectonic activities． Because of low hydrogen concentrations in fault rocks，absolute detection limit and stability are important factors in choosing the observation instrument． Experimental comparison study of two sets of trace hydrogen observation instrument in the same sampling location and under the same environment was carried out in the piedmont fault zone of Zhongtiao Mountain． The observed results show that two curves recorded by two instruments display almost the same changing tendency and forms with slightly differences on details． After the fitting analysis and correction by the correlation coefficient，two curves are nearly overlapped． This result reveals that the automatic trace hydrogen analyzer has good stability，high sensitivity，digitization，and consistence with the observed results，which is able to meet the needs of earthquake monitoring，and provide safeguard for the new observation technology of seismic precursor．