Using a recently developed Crystal structure Anal. by Particle Swarm Optimization' (CALYPSO) algorithm on a structural search, we predicted a novel sp3 carbon allotrope possessing an orthorhombic lattice with the space group Cmmm (oC32). The calcd. elastic consts. and the simulated hardness revealed that oC32 simultaneously possesses ultra-incompressible and superhard properties with a high bulk modulus of 457 GPa and a high Vickers hardness of 96.2 GPa. This oC32 phase is dynamically stable and energetically more preferable than the experientially obsd. cold-compressed carbon, thus oC32 is expected to be exptl. synthesizable under extreme conditions. These results further expand the list of meta-stable carbon allotropes and superhard materials under atm. and extreme conditions.