The utility model discloses a reinforced concrete caisson of a special-shaped box, which is characterized in that the caisson is in an asymmetric special-shaped box structure with a trapezoidal horizontal section, the caisson is divided into a plurality of sand stone stock bins by partition plates, and a ship-shaped backfilling bin with a round head is arranged at a small end of the caisson. Compared with the prior art, the reinforced concrete caisson has the advantages of more reasonable structural stress and less steel concrete material consumption, is particularly suitable for primary construction of a caisson structure in an earth cofferdam, and floats to a sinking site after overwater prefabricating and heightening of the box structure by the aid of tidal difference, thereby further reducing project cost, being simple and convenient in construction and short in construction period.