The invention relates to a method for elastically restraining main beam displacement of an ultrahigh-span cable-stayed bridge. The method comprises the following steps: after construction of main towers, arranging permanent supports on the top surfaces of main tower transverse beams; arranging zero segments of main beams; arranging temporary concretion between the main tower transverse beams and the main beams; assembling cantilevers with the main beams into largest cantilevers; before folding of the main beams, arranging spring devices on the top surfaces of the main tower transverse beams; connecting upper connecting plates of the spring devices with the bottom surfaces of the main beams, and connecting lower connecting plates with the top surfaces of main tower transverse beams; after folding of the main beams, removing the temporary concretion; performing subsequent construction. The spring devices are arranged among the main tower transverse beams of the ultrahigh-span cable-stayed bridge along the longitudinal direction of the bridge, elastic restraint is provided for the main beams by using the spring recovery force, and the main beams are controlled to perform longitudinal displacement under the action of static power load. The displacement of the main beams can be effectively controlled, the inner stress of the main tower is reduced, the extension and contraction amounts of a beam end extension and retraction device and a rail extension and retraction adjusting device are reduced, and the driving stability and safety of the bridge surface are improved. The method is applied to the Hu-Tong highway-railway dual-purpose cable-stayed bridge being 1,092 meters in length.