During the design of the suspension cables of the Third Bridge over the Bosphorus Strait in Turkey, the large deflection angle of the suspension cables at the limit position during the operation of the bridge was fully considered. It was required to design a flexible waterproof cover to seal the connection between the suspension cable and the cable guide pipe to protect the suspension cable anchor from rainwater corrosion. This paper designs the material selection and structure of the flexible waterproof cover, and verifies the mechanical performance and sealing effect of the flexible waterproof cover through theoretical calculation and ANSYS analysis.