Main girder closure is the key process for cable-stayed bridges to achieve internal force and alignment goals. Focusing on the stress problem of main girder closure during the construction of cable-stayed bridges, this paper analyzed the mechanical characteristics of different construction methods of simply supported closure of the main girder based on the adaptive unstressed configuration control method of bridges and established an analysis method for calculating the manufacturing size of closure segment in simply supported closure method. Moreover, it put forward a new intelligent incremental launching method for simply supported closure with Jiayu Yangtze River Bridge as the background and analyzed the main girder alignment and structural stress results after closure. Finally, it verified the feasibility of the proposed new closure construction method. The results show that the measured alignment is basically consistent with the theoretical alignment, and the proposed closure method has high operability and can ensure high closure accuracy.