Abstract: The shear transmission mechanism of new and old concrete interface with post-installed rebars is summarized, and the influencing factors of the interface shear capacity are divided into four categories: material property and size, interface treatment, reinforcement arrangement, and load action. The research on the interface bending moment and the interface size effect, which are less mentioned in codes, are summarized. An example of anti-floating calculation of a 2 m thick temporary bottom slab of subway station shows that these two factors may have great influence on interface shear capacity. The similarities and differences of shear transmission mechanism, interface roughness and interface bending moment, which are considered in the calculation of shear capacity of new and old concrete interface with post-installed rebars in the codes of China, Europe, America and Canada, are compared. It is suggested that the size effect should be considered when the code is revised.