The invention relates to the field of metallurgy and discloses low-alloy cast steel as well as a manufacturing method and application thereof. The low-alloy cast steel comprises the following components in percentage by weight: 0.22 to 0.29 percent of carbon, 0.20 to 0.40 percent of silicon, 0.61 to 0.79 percent of manganese, less than or equal to 0.020 percent of phosphorus, less than or equal to0.015 percent of sulfur, 1.00 to 1.10 percent of chromium, 1.10 to 1.20 percent of nickel, 0.61 to 0.81 percent of molybdenum, 0.02 to 0.06 percent of aluminum, 0.02 to 0.05 percent of niobium, 0.11to 0.21 percent of tungsten and the balance of iron and other unavoidable elements, wherein molybdenum+0.26*tungsten is more than or equal to 0.65 percent and less than or equal to 0.90 percent. The low-alloy cast steel can effectively inhibit the growth of austenite crystal grains in the heating process and refine the crystal grains, and can strengthen a substrate and improve the low-temperatureimpact toughness; furthermore the strength and the hardenability of the low-alloy cast steel are high. The manufacturing method of the low-alloy cast steel is used for manufacturing the low-alloy caststeel. The low-alloy cast steel can be used for manufacturing locomotive parts.