Abstract: The existing modular steel structures generally use a single type of modular connections, which ignores the stress behavior differences in different areas under earthquakes. This leads to the mismatch of connecting performances and limits applicability to connecting different types of modules, which is not conducive to achieving multiple functions of the structure. The friction-non-self-centering and friction-self-centering composite plug-in modular connections that meet various connecting requirements are proposed. Based on the force mechanism of the connection, a parameter design method for key components is presented, refined numerical simulations are conducted to investigate the hysteretic response, stress distribution, and energy dissipation capacity of the composite connections, and the working mechanism of the connections is revealed. Research results indicate that the different connecting methods of the composite connections can work stably and collaboratively. Owing to the additional energy dissipation provided by the T-stub-friction device, the energy dissipation capacity of the composite connections is enhanced by 21.8% to 30.6%, compared to that of plug-in and self-centering plug-in connections. The placement of T-stubs and self-centering haunch braces significantly influences the hysteretic performance of composite connections. The connections with T-stubs or haunch braces installed on the ceiling beam exhibit higher bearing capacity, fuller and more symmetric hysteretic loops. Due to the haunch braces, the friction-self-centering connections show increased stiffness and bearing capacity, along with educed damage in a connecting core region and with smaller residual deformations, compared to friction-non-self-centering connections.