The invention provides a high-level parallel pilot tunnel structure and a construction method for rebuilding the high-level parallel guiding tunnel structure into a double-line tunnel in an expanding mode so as to achieve the conditions that a large amount of abandoned projects produced by rebuilding construction in the expanding mode are effectively avoided, the construction safety risk is lowered to the greatest extent and project investment is greatly reduced. The high-level parallel pilot tunnel structure comprises a parallel pilot tunnel located at the position, away from the left side or the right side by 30-50 m, of an existing tunnel. The center line of the parallel pilot tunnel coincides with the center line of the later-period double-line tunnel. The bottom surface of the parallel pilot tunnel is located above the top surface of an inner rail of the later-period double-line tunnel. The inner outline shape of the fracture surface of the parallel pilot tunnel adapts to the inner outline shape of the fracture surface of the upper portion of the later-period double-line tunnel. An anchor-sprayed supporting structure is adopted in the parallel pilot tunnel arch wall range and serves as a permanent supporting system in the upper arch wall range of the later-period double-line tunnel. A model-building concrete bottom plate is arranged on the bottom surface of the parallel pilot tunnel, and a tunnel bottom drainage ditch is arranged on one side of the parallel pilot tunnel.