To monitor the Arsenic dynamic variations in fault gases and groundwater, five spring points were located at the north segment of the Red River fault in western Yunnan. For three years, we have conducted Arsenic observation, the results show that Arsenic changes are fairly relaxed to the moderately strong earthquakes in this region. With the example showing the relations in the M 7.6 Lancing earthquake, the Arsenic abnormal features in the seismogenic process and the abnormal mechanism are discussed. And the feasibility of applying Arsenic in earthquake prediction also is demonstrated.