Tunneling in completely weathered granite and its residual soil ground with compressed air can pre- vent seepage of groundwater into the tunnel and improve the stability of tunnel face. However, some problems exist such as the air pressure control in head chamber, and it is necessary to evaluate the rate of air loss with shield method using compressed air. In view of compressed air tunneling for a subway tunnel in Guangzhou, ac- cording to the characteristics of gas and soil movement in the soil and considering the strongly nonlinear of air and water conduction function in unsaturated soil, a three-dimensional finite element seepage model of layered homogeneity and isotropic soil was established by using TOUGH2 software. The basic rule of gas and water mi- gration in the stratum with A-EPB shield method was revealed. The research results show that an unsaturated zone has been formed and this zone progressively develops with time until it connects with the surface and forms a funnel shaped steady seepage channel. The calculated air losses are within the range from the field date, which verifies the rationality of this model. Finally, an exponential relationship has been conducted between permeabil- ity coefficient of soil and quantity flow of air seepage, and the air injection quantity of different soil layers has been suggested.