The invention relates to a main girder slide die carrier system and a construction method of cable-stayed bridges, with steps as follows: when the construction 0# segment is finished, a bailey truss sliding die carrier is extended, which is divided into three groups that respectively move forward to next row of supporting piers; a construction segment bottom die is dragged to place; a fore-fulcrum elevation of the die carrier is adjusted; suspenders are stretched ahead; segmental steel bars and prestressing tendons are bound; segmental concrete is poured; segmental pre-stressing tendons are stretched; the die carrier is down adjusted; the bottom die is moved forward to next segmental place; and the steps are repeated. The invention has the advantages that by using the stress system of front supporting and back cable staying, one part of load has transferred to a cast girder segment, and the other part is borne by temporary piers, stressing is definite, calculation is easy, working condition is unified, and main girder linear adjustment control is convenient. The invention is applicable not only to concrete connecting girders and T-frames, but also to cable-stayed bridges with various cross-sectional shapes, achieves single cable plane, small transverse stiffness, wide flange plate cross section main girder, and whole section global casting, saves labor and materials, enjoys a short construction period and standardized construction, and is stable, safe and reliable.