The invention provides a sleeper structure and construction method for bonding old and new concrete on a ballastless track. The sleeper is divided into the upper part and the lower part in the cross section, the upper part 1 is in a rectangular shape, the length of the upper part 1 is l1 and the height of the upper part 1 is h1. The step-slope upper part 2 of the sleeper is in an isosceles trapezoid shape, the upper side of the upper part 2 is longer than the lower side of the upper part 2, that is, for the lower part of the sleeper, the adopted gradient of a bottom surface step-slope part side 4 of a step slope toward the inside is 1:1; the length of the upper side of the isosceles trapezoid is l1, the length of the lower side is l2, the horizontal length l2 of a sleeper bottom surface 5 is controlled to 8-10 cm, the height h2 of the lower part 2 is shown as follows: h2=(l1-l2)/2, and the total height h3 of the cross section of the sleeper is as follows: h3=h1+h2. The construction method includes the steps of 1, preparing a sleeper mold, 2, connecting steel bars in the sleeper and the sleeper with truss bars, 3, pouring sleeper concrete, 4, processing reinforcing steel bars of the whole roadbed slab according to a design drawing, 5, bundling the reinforcing steel bars of the whole roadbed slab, 6, conducting concrete pouring on the whole roadbed slab, 7, maintaining the concrete, 8, disassembling formworks and tool rails.