The invention relates to a water electric-conductance air doping measurement instrument. The measurement instrument comprises an electrode for setting and standardizing a conductance cell, wherein the electrode is connected with a signal acquiring circuit, the signal acquiring circuit is connected with a standard correction circuit, the standard correction circuit is connected with a signal output circuit and an A/D conversion circuit, the A/D conversion circuit is connected with an operational circuit, and the operational circuit is connected with a display circuit. By supposing that liquid water and air are infinite uniform mediums respectively with intrinsic conducting properties, liquid water and air can be uniformly mixed in any volume ratio to form homogenized conductor and can be freely separated to generate mutually independent original states. A uniform weak electric field is formed in the conductance cell standardized by a pair of planar electrodes which are relatively parallel to each other and have fixed dimensions, so as to deduce that the comprehensive conductance of a uniformly doped gas-water two-phase fluid is in positive correlation with the volume of a water-phase medium in the gas-water two-phase fluid. By establishing a formula for calculating a linear volume air doping concentration through a conductance ratio, the calculation accuracy is increased, and the calculation process is greatly simplified.