The existing international submarine cable system and terrestrial cable transmission system are designed independently according to their respective specifications, the two types of systems are connected through back-to-back method in the submarine cable landing station. In view of problems of relatively high investment and operating costs problems in existing methods, this paper elaborates the developing requirements of the joint network design of the submarine cable and terrestrial cable optical transmission system. Based on the analysis of the design specifications of submarine cable system and terrestrial cable system, it is suggested to use the generalized signal-to-noise ratio index to measure the overall transmission system performance. Finally, the joint design of the submarine cable and terrestrial cable optical transmission system is studied based on examples, deploying suggestions are given as well.noise ratio