The invention provides a shutting method for a midspan section of a double-tower double-cable plane mixed steel-concrete superposed beam cable stayed bridge. The method comprises steps of cutting margins for a midspan section shut section according to a determined shut port length, refiting a hoisting apparatus to enable the hoisting apparatus on one side to work as a main hoisting apparatus, thereby forming a work platform for on-site installation of the midspan shut section, drilling and pre-splicing on site for the midspan shut section, permanently connecting the midspan shut section undera determined shut condition, installing a bridge panel on the well-connected midspan shut section to form a midspan bridge plane, installing and pulling prestressed steel beams on the midspan bridge plane, and removing the hoisting device and temporary fixing and connection assemblies until the completion of the construction of the midspan shut section. Effects of deformation of a steel beam section to construction is strictly controlled in the midspan shutting method, so construction precision can be improved; and procedures are simplified and error occurrence rate is reduced.