The invention relates to a nodular cast iron gear box with high impact toughness at ultralow temperature. The nodular cast iron gear box comprises, by mass, 3.50-3.80% of C, 1.7-1.9% of Si, 0.10-0.15% of Mn, 0.035% or less of P, 0.015% or less of S, 1.0-1.3% of Ni, and the balance of Fe and inevitable impurities. A making method comprises the following steps: melting highly pure Q10 pig iron, Q235 carbon structural iron and returns in an intermediate frequency induction electric furnace, adding nickel plates, and adjusting the percentages of all chemical components; nodulizing by adopting an exposure ladle pour-over technology, and sequentially packing a nodulizing agent, an inoculant and a covering agent in a layered manner; and carrying out primary stream inoculation during tapping, carrying out ladle inoculation, and carrying out secondary stream inoculation during casting. The making method improves the elongation and the low-temperature impact toughness, reinforces the matrix structure, guarantees reasonable graphite sphere number and high nodulizing rate, improves the toughness and plasticity, does not need graphitization annealing heat treatment, and saves the production cost.