The invention provides a prefabricated assembled caisson. The prefabricated assembled caisson comprises a ring well body and a plurality of tubing bolts, the ring well body comprises at least two arc-shaped well pieces, first arc round holes are formed in the two opposite sides of the well pieces, the first arc round holes in the two adjacent well pieces in the circumference direction communicatewith each other, and the tubing bolts penetrate through the first arc round holes to fix and connect the two adjacent well pieces. When the prefabricated assembled caisson is transported, the tubing bolts can be loosened in a screwed mode to remove the two adjacent well pieces, the transporting space occupied by the prefabricated assembled caisson is reduced so as to transport more prefabricated assembled caissons to reduce the transporting cost; when the transported well pieces reach to a designated location, the two adjacent well pieces can be quickly assembled and connected through the tubing bolts, and then the ring well body is installed in the caisson construction place and sunken; and compared with the site pouring concrete, the construction is simple and convenient, the construction efficiency is improved, in addition, the invention further provides a caisson construction method.