The invention discloses a method for preparing a forging mould by double-layer metal resurfacing welding based on a cast steel substrate. In the invention, cast steel is utilized as a forging mould substrate, a wave-shaped substrate surface is formed, double-layer metal resurfacing welding is carried out on a substrate layer, then tempering is carried out to remove stress, and finally, a mould is processed and formed by a machine. The invention provides a method for preparing the forging mould, which can better meet the performance requirements of a mould of the forging mould in the aspects of the hardness, the strength, the toughness and the like and also can decrease the production cost; the invention realizes the manufacture and use of the mould with low cost, low energy consumption, short time, high utilization rate, high efficiency, high performance and high benefit and has an imponderable meaning for the mould industry.