Abstract: This paper introduces the basic situation of a deep soft soil foundation in the south linkage expressway engineering of the Hangzhou Bay Cross-sea Bridge. Through the preliminary studies of the pilot experimental sections, a principle design scheme and the fine design and calculation methods, construction technology, construction management as well as the quality control measures for the deep and thick soft soil foundation treatment were proposed and discussed, which forms a complete technology for the deep and thick soft soil foundation treatment of the expressway. And the soft soil foundation treatment of the south linkage expressway of the Hangzhou Bay Cross-sea Bridge and other expressways in the Ningbo region was finished by the use of the complete technology. The analysis of the foundation treatment effects is carried out in this study, and from the construction practices it is found that this complete technology for the deep and thick soft foundation treatment has been successfully applied to the similar works, which shows that the application effect of the deep and thick soft soil foundation treatment technology is relatively ideal.