The invention discloses a no-balance-weight horizontal-rotation construction method of a steel truss girder bridge spanning a railway operating line. The construction method comprises the following construction steps: 1) the design and the construction of a rotation body facility at the rotating end is conducted, wherein the rotation body facility at the rotating end comprises a rotation body running track girder and a pier top facility No.25; 2) the design and the construction of a rotation body facility at the rotating shaft end is conducted, wherein the rotation body facility at the rotating shaft end comprises a positioning shaft, a bearing arm brace, a slide ship, a slide way and a pier pillar widening structure; and 3) the design and the construction of a rotation body running mechanism is conducted, wherein a rotation process adopts a walking type incrementally-launching running mechanism, and the running mechanism comprises the slide ship, a slide groove, an incrementally-launching hydraulic oil cylinder and an incrementally-launching counterforce device. Through technical economy comparison and selection, the invention adopts the construction scheme that a steel truss girder is assembled at a high level on the lateral side of the railway operating line by using a bracket method, and the girder is lowered and emplaced after being rotated to a design position by using the no-balance-weight horizontal-rotation method.