To provide a gas-liquid mixing method capable of producing a highly concentrated liquid solution.

The gas-liquid mixing method produces the liquid solution W of a gas G by dissolving the prescribed gas G in a prescribed liquid L through a preliminary mixing process, a 1st dissolving process and a 2nd dissolving process. In the preliminary mixing process, a preliminary mixed liquid P1 allowing the bubbles of the gas G to coexist in the liquid L is produced by an ejector 6. In the 1st dissolving process, the gas G is dissolved in the liquid L by applying pressure to the preliminary mixed liquid P1. In the 2nd dissolving process, the dissolved liquid W is produced by allowing the gas-liquid mixed liquid P2 to flow in a mixing vessel 1 through the 1st dissolving process so as to generate a voltex flow and by dissolving the gas G in a state of the remaining bubbles B into the liquid L.