Abstract: This paper analyzes the causes of leakage at construction joints of tunnel linings, and describes the development of a X-type drainable waterstop with a butterfly-shaped section based on the middle-buried drainable waterstop and the standard built-in back-paste waterstop. The head of the butterfly-shaped waterstop should be installed toward the water side of the construction joint and the waterstop should be pressed toward the end formwork of the lining section from the side (one side of the lining is cast first), making the wing part at another side of the later cast lining section deform to press upon the end formwork. The waterstop is then fixed by a steel nail with a gasket point to point at proper intervals from the rib. The first cast lining section is stripped after curing for some time and the wing part of the waterstop is restored with the help of the elasticity of material. The advantages of the X-type drainable waterstop are: easy installation, the high quality of the waterstop construction, and impermeability at both sides of and the top of the tunnel. Additionally, leakage is reduced due to the waterstop's function under low pressure or no pressure.