The present invention discloses an ultra-high strength and ultra-high toughness casing steel, having a microstructure of tempered sorbite, and the content of chemical elements by mass percent thereof being as follows: C: 0.1-0.22%, Si: 0.1-0.4%, Mn: 0.5-1.5%, Cr: 1-1.5%, Mo: 1-1.5%, Nb: 0.01-0.04%, V: 0.2-0.3%, Al: 0.01-0.05%, Ca: 0.0005-0.005%, the balance being Fe and unavoidable impurities. Correspondingly, the invention also discloses a casing obtained by processing the ultra-high strength and ultra-high toughness casing steel and a manufacturing method thereof. The ultra-high strength and ultra-toughness casing steel and the casing of the present invention have a strength of 155 ksi or more and an impact toughness greater than 10% of its yield strength value, thereby realizing a combination of ultra-high strength and ultra-high toughness.