Abstract: Based on a 3 GW DC offshore wind power project, design and experimental verification of a ±550 kV high-temperature cross-linked polyethylene (XLPE) insulated DC submarine cable were presented. Firstly, fundamental dielectric properties including space charge characteristics, high-field DC conductivity, and DC breakdown strength were tested on insulating material used for high-temperature DC submarine cables. Reliability of insulating material was verified, and functional relationships between conductivity and electric field strength as well as operating temperature, together with characteristic curves of electric field strength versus operating temperature and insulation thickness, were analyzed. Based on dielectric performance test results of insulating material, cable structure design, degassing process study, and factory joint process investigation were carried out. Transmission capacity and electric field distribution were calculated under an operating temperature of 90 ℃. Finally, type tests for the ±550 kV high-temperature XLPE insulated DC submarine cable were conducted at 90 ℃ in accordance with GB/T 31489.1—2015 and CIGRE TB852:2021. Results showed that during load cycle test, conductor temperature of the developed ±550 kV DC submarine cable reached 90 ℃, and under the operating temperature of 90 ℃, both long-term operating electric field strength and overvoltage levels met the requirements.