Abstract: To address the high-voltage, large-capacity power transmission requirements of deep-sea wind farms, as well as the technical bottlenecks of DC submarine cables in deep-sea DC transmission projects, a ±640 kV large-cross-section DC submarine cable was successfully developed through feasibility calculations for centralized transmission schemes, performance verification of DC insulation materials (including space charge characteristics), optimization of key production processes, and simulation/experimental verification of 90 °C current-carrying capacity. Results demonstrated that insulation material of the cable exhibits an electric field distortion rate of only 4.3% under an applied electric field strength of 20 kV·mm^–1, significantly outperforming the national standard requirement of less than or equal to 20%. Additionally, electric field strengths at conductor shield and insulation shield were 21.28 and 21.48 kV·mm^–1, both below the insulation material's working field strength limit of 30 kV·mm^–1. Current-carrying capacity under various laying conditions were exceeded the minimum required for transmitting 3 000 MW, fully meeting design requirements of the designed DC submarine cables. Additionally, the cable passed lightning impulse voltage and DC voltage performance tests, validating its stable and reliable operation. This research provides technical support and reference for the engineering application of extra-high-voltage flexible DC submarine cables and deep-sea wind power grid integration projects.