The invention provides ultra-high chromium cast iron and a preparation method thereof. The ultra-high chromium cast iron provided by the invention comprises the following components by mess content: 2.55 to 2.75% of C, 0.7-1.5% of Si, 0.5-1.5% of Mn, 40. 5 to 45.0% of Cr, 1.0 to 3.0% of Mo, 1.0 to 3.0% of Ni, 1.0 to 2.0% of Cu, 0.2 to 0.5% of Ti, and 0. 2 to 0.5% of V and the balance of Fe. By increasing the contents of carbon and chromium, as well as the content of carbide in the material, the hardness is improved on the premise of not reducing the corrosion resistance, so that the service life is further prolonged; and due to the addition of titanium and vanadium, the treatment is refined to avoid the reduction of toughness. Experimental results show that the hardness of the ultra-high chromium cast iron provided by the invention can reach 51.7 HRC, the impact toughness can reach 5.7 J/cm<2>, and the corrosion rate in 45% phosphoric acid is less than 0.05mm.a<-1>.