The invention provides an alloy cast steel, as well as a manufacturing method and application thereof. The alloy cast steel is prepared from the following components including, by weight, 0.12 percentto 0.21 percent of carbon, 0.15 percent to 0.35 percent of silicon, 1.21 percent to 1.50 percent of manganese, less than or equal to 0.035 percent of phosphorus, less than or equal to 0.035 percent of sulfur, less than or equal to 0.25 percent of chromium, 0.31 percent to 0.56 percent of molybdenum, 0.02 percent to 0.04 percent of aluminum, 0.02 percent to 0.04 percent of niobium, less than or equal to 0.020 percent of nitrogen, and the balance iron and other inevitable elements. The cast steel prepared from the cast steel materials contains the appropriate amount of carbon, manganese, molybdenum and chromium, so that the strength of the cast steel is improved; and meanwhile, by controlling appropriate contents of other elements to achieve cooperation, on the premise that nickel is adopted, the strength of the cast steel is improved, and the low-temperature toughness of the cast steel is improved.