Suspended ceiling structure of long span underground powerhouse and construction method thereof

The invention discloses a suspended ceiling structure of a long span underground powerhouse and a construction method thereof. The suspended ceiling structure of the long span underground powerhouse comprises two equilong rock anchor beams which are constructed and completed are located on two sides of an upstream and a downstream, a steal arched beam is located between the two rock anchor beams and stretches across in the upstream and downstream directions, an arched waterproof layer purlin support and an arched waterproof layer purlin strip are supported at the top flange of the steal arched beam, and an arched waterproof board is fixed to the arched waterproof layer purlin strip; a plurality of steel hanging rings and steel hanging rods are hung on the bottom flange of the steal arched beam, a main runner of a horizontal decorating layer is hung under the steel hanging rods, and a horizontal decorating layer purlin strip is fixed under the main runner; a fixed decorating board is installed on the lower surface of the horizontal decorating layer purlin strip, a plurality of air conduits are arranged in space between the horizontal decorating layer and an arched waterproof layer, and a plurality of maintenance trestle roads along cliffs are installed on the upper surface of the main runner. The steel arched beam and all steel components can be conveyed to a site to install after being processed, manufactured and completed in a factory, the construction is convenient, and the construction period is shortened. The water seepage of a powerhouse top arch is drained to an upstream and downstream side wall drainage ditch from an upper layer of the waterproof board, the problem that the top arch leaks water is solved, a decorating role of a lower layer of the horizontal decorating layer is played, and the operating requirement of power station is met.