Abstract: Geological logging-while-drilling makes an accurate judgment only for the single pressure layer, but while meeting multiple pressure layer series during the exploration well drilling that will affect the accurate judgment of the position of the gas reservoir due to lower layer cuttings will be polluted by the gas of the upper layer. In accordance with the characteristics of Flow-Drilling under balance pressure drilling, we establish the gas invaded model and conduct theory derivation. It determines the position of the gas reservoir by measuring the changes of the bottom pressure and temperature while drilling operation. Because the bottom pressure and the temperature data are measured at the first time of drilling in the gas reservoir so that the method can determine the position of gas reservoir in different pressure layer series quite accurately. This can remove the error of the geological logging and log interpretation. Well completing test shows that this method is very accurate and provides a new means for the exploration of multiple pressure layer series in deep zone.