The utility model relates to a new interface and old interface connecting structure. The connecting structure comprises a newly-built concrete side wall, an existing concrete side wall and a connecting assembly used for connecting the new concrete side wall and the old concrete side wall. An installation gap exists between the newly-built concrete side wall and the existing concrete side wall. Theconnecting assembly is mounted in the mounting gap; the connecting assembly comprises an installation plate installed on the newly-built concrete side wall, a positioning plate installed on the sidewall of the existing concrete side wall, water swelling water stop strips arranged on the side wall of the installation plate and the side wall of the positioning plate and a covering plate covering the installation plate and the positioning plate, and a grouting opening is formed in the top of the side wall of the covering plate. The utility model has the effects that the connection between new and old interfaces is facilitated, the connection process is simplified, the construction period is shortened, and the enterprise benefit is improved to a certain extent.