Abstract: The technology of patching outside casing is conducted through tie-back and seal from the original casing externally, without losing the original inside diameter of the casing, without any disadvantage influence on the follow-up drilling operation. Meanwhile, the casing patch tools with different sizes and pressure can meet the requirements for different casing program and drilling platform. In this article, an introduction has been given on the characteristic of technology for patching outside casing, the process and implementation steps of the tie-back outside casing, which can provide references for dealing with similar casing processing in the future. In addition, two application examples in the western part of South China Sea have been given in this paper, and the application results indicated that technology of patching outside casing can be used effectively to solve the problems when casing is not in place or well-head equipment has troubles.