Abstract: Abandonment pressure and recoverable reserves are the key parameters to determine recovery efficiency of a gas reservoir with water influx. Their values directly affect gas recovery efficiency. Therefore it is so important to obtain accurate data of abandonment pressure and recoverable reserves for a gas reservoir with water influx. This article presents the imaginary line method. First we can derivate the equation of pseudo abandonment pressure and recoverable reserves using volumetric method. Then plot p/z curve and imaginary line by applying the production performance data, the two curves will bring up an intersection, this intersection is the abandonment point, then we can calculate abandonment pressure and recoverable reserves using this abandonment point.