The invention discloses an oversized caisson installation process which includes the following steps of (a) positioning small caissons, (b) filling sand into the small caissons, and increasing the self weights of the small caissons so that the small caissons can be firmly positioned, (c) arranging a positioning boat between two small caissons, and installing a winch on the positioning boat, (d) stopping the boat and tying mooring ropes, arranging a winch on a large caisson, and tying the mooring ropes onto the two small caissons and the positioning boating respectively by controlling the direction and the position of the large caisson through a tugboat, (e) carrying out rough positioning of the large caisson, and (f) carrying out fine positioning of the large caisson. According to the oversized caisson installation process, the large caisson is positioned and installed with the assistance of the small caissons, so that installation precision of the oversized caisson is greatly improved, and successful one-time installation of the oversized caisson is guaranteed; the large caisson is positioned and installed with the assistance of the tugboat, the tugboat is used for controlling the speed of the oversized caisson approaching the small caissons, adverse influences of sea conditions are overcome, impact force to the small caissons is reduced, and installation speed is increased.