Abstract: The stability of deepwater surface casing directly determines the safe and effective implementation of follow-up drilling and oil producing operations. Cementing is the foundation to guarantee the safety and stability of deepwater surface casing. The paper analyzes frequent complex cases such as flagpole injection and failed pressure test after cementing and concludes that the effective replacement of inner string (fiberglass pipe) is the key factor that contributes to these complexities. The conclusion is proven in the replacement analysis enabled by large finite element software. A new side-hole fiberglass piping structure is developed and the three-dimensional finite element simulation analysis shows that the new structure can effectively avoid the defects of the existing structure to prevent complex conditions like flagpole injection or cement mixing, supporting the further promotion and application of the new structure.