The invention relates to a method for making a trench wall in the soil, in which a trench wall cutter having at least one rotatably driven cutting wheel is lowered into the soil, whereby soil material located below the cutting wheel is stripped and a cut trench is made and a settable liquid is supplied into the cut trench. For this purpose it is intended that a gas is supplied into the cut trench. The invention further relates to a trench wall cutting device for making a trench wall.