The invention relates to a straddle method of a cantilever of a long-span simply supported steel truss beam of the horizontal curve section. The straddle method comprises calculating the lengths of main truss rods arranged on the inner side and the outer side of a cantilever span curve and main truss rods arranged on the inner side and the outer side of an anchor span curve according to the radius of a horizontal curve, the position on the horizontal curve of a bridge span structure and the main truss spacing; hoisting the main truss rods arranged on the inner side and the outer side of the cantilever span curve to the position of a permanent support arranged at the top of an Nth pier, enabling the permanent support arranged at the pier top and the main truss rods arranged on the inner side and the outer side of the anchor span curve to be connected together through a temporary connection structure and performing cantilever construction of steel beam rods along the design axis; removing the temporary connection structure after the bridge span is straddled in place. According to the straddle method of the cantilever of the long-span simply supported steel truss beam of the horizontal curve section, the horizontal pushing in-place operation of the steel beam in the process of construction is avoided successfully, the construction process is simplified, the straddle construction of the cantilever of the long-span simply supported steel truss beam of the horizontal curve section can be greatly simplified, the stress is reliable, the construction is convenient, the operation is simple, temporary construction facilities and field workloads of the pier top are reduced, the construction progress greatly speeds up, the construction cost is saved, and the economic benefit is remarkable.