Light lowering system for old bridge demolition and construction method of light lowering system

According to the light lowering system for old bridge dismantling and the construction method of the light lowering system, the light lowering system is arranged at bridge piers on the two sides of a first-span main beam, the structural size of the light lowering system is matched with the size of the first-span main beam, and the light lowering system is small in occupied size, can adapt to main beam dismantling operation with narrow environment space and can be rapidly carried and moved through a crane; the problem of unbalanced connection and support between adjacent span main beams is solved by arranging the leveling connection system, and the span middle beam sections of a plurality of precast beams can be dismantled and lowered to the arranged ground supporting system at a time through the bearing beam system and the hydraulic lowering system which are longitudinally arranged above the bridge span and are supported at the beam top of the bridge pier. And a plurality of groups can be arranged on the brid