To solve the joints at the interface between the main body and the ancillary structure of the subway station cannot be pre embedded with embedded waterproof components, the author and their team have developed a slot type polymer coated waterstop and its supporting products and construction technology. The internal core material of the waterstop is made of 1 mm thick steel plate pre processed into a “T” structure, surrounded by 1.2 mm thick polymer waterproof and anti-corrosion coating. Using matching fixing glue to fix the cold joint section, using matching “L”-shaped connecting plates and matching connecting glue to connect the waterstop into a ring, achieving the middle buried waterstop of the cold joint. This new waterproofing solution has been tested in the laboratory and proven to effectively solve the problem of interface cold joint leakage in underground projects such as subways and civil air defense in Beijing, Xuzhou, Zhoukou, and other areas. It has good promotion and application significance and can be used as a reference for similar projects.