The application discloses a method for connecting an ultra-high-
voltage and large-capacity
submarine cable on a sea site and an installation platform thereof, and the method comprises the following steps: step 1, preparation before construction; step 2, approach of a leg
pile lifting type water mobile installation platform; step 3, platform
pile insertion positioning; step 4, self-lifting height adjustment; step 5, expansion of a
submarine cable chute; step 6, salvage of a
submarine cable end and fixation; step 7, erection of a joint manufacturing room and a purification room on the platform; step 8, cable end connection; step 9, installation of a cable soft joint protector; step 10, installation of a bending
limiter; step 11, hoisting and launching of a joint; and step 12,
pile pulling and site leaving. In the method, the installation platform is lifted to reduce the
impact of
sea waves, so that the platform is more stable, and the method has the characteristics of safety and reliability and high connection efficiency. The cable soft joint protector is improved, long-term protection function is realized, and the maintenance cost is reduced.