Abstract: In order to improve the earthquake-reflecting ability of the fault soil gas CO₂ content data,critical issues from 4aspects of test point selection,equipment layout,observation method,auxiliary items rapid determination method of fault soil gas CO₂ content was studied,the conclusion: (1)the fault soil gas CO₂ content measuring points should be selected in the rupture of active fault zone or adjacent to the crack sensitive zone,study or the effective detection of underground rock structure in the test point selection should be combined with the data of geological data and drilling on the location and the rupture of degree, not choose CO₂ content measured point in the existing seismic stations only for observation convenient; (2) device used in the determination method of the fault soil gas CO₂ content should layout as deeper as possible in underground,measure hole depth should be deeper than 0.5mbelow the surface,the beset depth is 2.0mor more so as to minimize or avoid the affection of surface biological layer,the underground water level should be taken into account,After the completion of the plant layout backfill soil compaction is necessary; (3)Artificial factors should be eliminated,especially the rapid determination tube should be placed near the bottom of the measuring hole but should not get in touch with the bottom,to rapid determination pipe bottom caliber should be consistent with each other so as to maximize the caliber; (4)Temperature of measuring hole and fault soil gas CO₂ changes were positively correlated,rainfall values have a negative influence on fault soil gas CO₂ content,temperature and rainfall aided synchronization observation is necessary. In view of changes in air pressure and fault soil gas CO₂ content has a strong negative correlation;further study on the mechanism of this effect is suggested.At the same time,the humidity should be measured as auxiliary observation of fault soil gas CO₂.