The invention discloses a method for manufacturing a flexible joint of a submarine cable capable of satisfying the requirements of high-voltage and ultrahigh-voltage use situations. The method comprises the steps as follows: 1) conductor connection; 2) conductor shield and vulcanization; 3) insulation extrusion; 4) insulation vulcanization; 5) insulation shield and repair; and 6) metal sheath recovery, wherein the insulation vulcanization process is that an insulated cable is put into a vulcanizing mould, nitrogen gas filled into the vulcanizing mould during the vulcanization cannot leak, cooling water systems at the two ends of the vulcanizing mould are simultaneously kept unblocked, so as to keep the temperature at the two ends of the cable below 70 DEG C; when the temperature reaches 235 to 245 DEG C and the nitrogen gas pressure is 1.5Mpa, insulation vulcanization begins, and the temperature and the pressure are regulated through a valve and a power source; and after the vulcanization is conducted for 120 minutes, the power source is cut off, the temperature is reduced below 100 DEG C while the pressure is kept at1.5Mpa, gas is discharged to release the pressure, and when the pressure is zero, the vulcanizing mould is opened and the cable is taken out. When the cable produced by adopting the manufacturing method disclosed by the invention is used as the submarine cable in high-voltage and ultrahigh-voltage situations, the performance of the cable is excellent and the requirements of the use environments are satisfied.