Active support method used for tunnel crossing existing bridge

The invention provides an active support method used for a tunnel crossing an existing bridge. The method comprises the steps: S1, before tunnel crossing construction, a jacking system with a plurality of arranged jacking apparatuses is adopted for actively jacking the bridge; S2, the jacking amount of the bridge subjected to the step S1 is monitored to judge whether the jacking amount meets an active jacking amount requirement; if not, the step S1 is repeated; if so, the bridge is firstly raised by adopting supporting seats, and then girder falling is carried out so as to prepare for the tunnel crossing construction. According to the invention, before the tunnel crossing construction, active jacking is carried out according to the bridge setting amount which is possibly caused by the tunnel crossing construction, even if the bridge subsides after the construction, the bridge can be still maintained within a safe range, and the hazards of stress, cracks, sedimentation and the like of the bridge caused by the tunnel crossing construction are avoided; and the potential safety hazard problem of the bridge caused by the construction can be solved by the active jacking.