The sealing effect of cofferdam will affect directly the safety and construction progress of the follow-up construction. Both the vertically laid plastic and high-pressure jet grouting are new waterproof curtain technology for the cofferdam developed in recent years. Any single sealing method is unfavorable for the deepwater seawall cofferdam in the area with a greater tidal range, thus a joint sealing method shall be adopted to meet the requirement. This method is expounded based on the design and construction of the joint sealing curtain of vertically laid plastic and high-pressure jet grouting in the special marine environment in the Jixing dike opening renovation project.