In this paper,we introduced the anomalies of fault-gases Rn,Hg and H₂ at Jiayuguan station be-fore the south Jiayuguan M5.4 earthquake. By comparing with the seismicity and leveling survey across the faults,it is shown that the anomalies are indeed the precursor of this earthquake. By study-ing the features of geological structures at the observation point,it is considered that Jiayuguan fault-gases correspond well to many earthquake because the point is situated in the position where the struc-tures are sensitive to multi-way force sources.