The invention discloses a steel-coal-seam long wall face non-pillar coal mining method. The method comprises the steps of (1) excavating an upper crossheading roadway and a lower crosshead roadway; (2) mounting a constant-resistance large-deformation anchor rod, processing a row of vertical energy-gathering blasting holes, and implementing blasting and presplitting; (3) erecting a column body for supporting a top plate, and arranging a protective layer on the back of the column body; and (4) carrying out recovery, slipping the top plate of a recovery face along a presplitting kerf; (5) withdrawing the column, hanging a net and spraying concrete to form a support layer; (6) mounting a slip-casting constant-resistance long anchor rod, and grouting; (7) forming a roadway automatically in the original crosshead roadway and taking the roadway as the upper crosshead roadway of the next mining face; and (8) repeating the steps (2)-(7). According to the method, the top plate at a worked out section collapses along the presplitting kerf, and meanwhile, a lower crosshead top plate is prevented from being damaged, and small caving waste rocks are prevented from entering the lower crosshead roadway, so that the roadway is automatically formed in the original crosshead roadway.