The invention discloses a turning construction method of a main beam of a mobile formwork bridge building machine. The construction method comprises the steps of 1, construction of a turning construction site; 2, disassembly of the main beam of the mobile formwork bridge building machine before turning; 3, turning of an N-th beam body, wherein 301, the N-th beam body is transferred between an original construction site and a turning area, 302, the N-th beam body turns in the turning area, and 303, the N-th beam body is transferred between the turning area and an assembly area; 4, turning of anN-1-th beam body, wherein 401, the N-1-th beam body is transferred between the original construction site and the turning area, 402, the N-1-th beam body turns in the turning area, and 403, the N-1-th beam body is transferred and assembled between the turning area and the assembly area; 5, repeating of the fourth step multiple times until turning of the main beam of the movable formwork bridge building machine is completed. By means of the method, a lot of labor and construction period are saved in the whole disassembly and assembly processes, the input of auxiliary equipment can be reduced,and meanwhile the construction efficiency can be improved.