Abstract: In this paper, through large quantity of exam ples, the gas function in the underground fluid of the earthquake m acroscopicanomalies is discussed. The variation of gas com position and content in groundwater can cause a series of physical and chemical reaction, as an importantreason, it produces the anomalies of underground fluid. With the gas chemical reactions, some chemical elements movedordeposited, and then cause the groundwater to become muddyor change colors. The gas spilling can make notable variation of the groundwater flow, water level and temperature. Gas relea sing from groundwater before an earthquake can reach large quantity and scale.

Key words: Underground fluid, Macroscopicanomaly, Gas