The invention discloses a shield tail sealing grease for a high water pressure resistant shield and a preparation method thereof. The grease is composed of the following components in percentage by weight: 8-18% of base oil 150N, 10-30% of polyisobutene, 10-30% of lithium-based grease, 1-10% of organic bentonite, 2-6% of lignocellulose, 1-5% of mineral fiber, 20-40% of calcium carbonate, 5-10% of barium sulfate and 5-10% of talcum powder. The shield tail sealing grease for the high water pressure resistant shield provided by the invention can be resistant to the water pressure of 6MPa at the temperature of 25 DEG C in a laboratory, and still has good pumping performance, with a price that is only 60% of that of an imported product. In construction of an actual shielding site, the shield tail sealing grease can be resistant to the high water pressure of 0.45-0.65MPa, meanwhile is excellent in comprehensive performance, and meets requirements of shield tail sealing in construction of high water pressure shield tunnels cross rivers and seas.