Abstract: Basing on the distribution features of the radon concentritions in the rock, water and gas before and after shocks, and release of groundwater (gas) on some active fauts, we propose a decay mechanism of groundwater (gas) as carrier of change in radon concentritions in water and gas, and point out that the radon concentritions in water and gas are connected with flow rate of groundwater (gas) and non-uniform distribution of radon in rocks and groundwater. Thus, it is suggested as a sensitiver precursor singnal responding to earthquakes. In the case of two-phase flows composed of waterphase and gas-phase, radon concentritions in groundwater and gas also are connected with distribution of radon in water-phase and gas-phase. When radon concentritions in two phases are simultaneously observed, more information on the variation of stress and strain and associated effects can be obtained.