Abstract: The composite shell lining (CSL) becomes more popular and a kind of main types of linings in conven? tional tunnelling in China. But there are some misunderstandings on how to design a composite lining structure and especially on how to control the engineering quality of CSL. The effectiveness of primary support was emphasized and some key points concerning the design of secondary lining were presented in this paper. As to the key point of CSL engineering quality control, it described that attention ought to be focused on a good fit of primary support, secondary lining and waterproofing membrane, and the flexibility index of waterproofing membrane was proposed based on the evenness of substrate surface, a contrastive analysis on the advantages and disadvantages was conducted regarding the spray-applied waterproofing membranes and hanging waterproofing sheets.