Abstract: With further development of deep-sea wind power, application of high-voltage and large cross-section submarine cables is becoming increasingly widespread, which raises higher requirements for quality control levels of cable manufacturing companies. Roundness is an important technical indicator to judge the quality of cables, especially for high-voltage submarine cables laid in deep sea. Good cable roundness will greatly improve its long-term operation reliability. In view of poor roundness in production process of high-voltage submarine cables, reasons and difficulties in improving the roundness of cables were analyzed and expounded. Combined with production practice, improvement measures for vertical continuous vulcanization (VCV) production line in terms of tooling equipment and process control technology were proposed. Results showed that for the optimized 220 kV cables, the roundness was improved from 98.0%~98.5% to 99.0%~99.5% for the 400 mm² and 500 mm² types, and from 98.0%~98.5% to 98.5%~99.0% for the 1000 mm² type, which indicated that the roundness of high-voltage submarine cables was significantly improved. Through systematically process optimizing and equipment improving, effectiveness of the above technical measures in enhancing geometric accuracy and production stability of high-voltage submarine cables was verified, which could provide manufacturing foundation for ensuring the long-term reliable operation of deep-sea power transmission systems.