To investigate the failure mechanisms and damage behaviour of composite steel-concrete columns under seismic loading, this study fabricated nine composite column specimens. Through low-cycle repeated loading tests, the seismic damage characteristics and hysteretic performance indices of the composite columns were examined. The influence law of parameters such as the width-to-thickness ratio of square steel tubes, reinforcement ratio, axial compression ratio, and recycled aggregate replacement rate on the hysteretic performance of composite columns was also studied in detail. Building upon these findings, and considering the influence of maximum displacement deformation and hysteretic cumulative energy dissipation on the seismic damage performance of composite columns, the coefficients of the Park-Ang seismic damage model were modified using an inversion method. This led to the development of a computational model consistent with the seismic damage characteristics and patterns of composite columns, enabling a deeper analysis of the evolution of seismic damage indices under varying design parameters. Based on these findings, the performance levels of composite columns were categorized into five grades: normal serviceability, temporary serviceability, serviceability after repair, life safety, and collapse prevention. Integrating the structural condition levels with seismic damage indicators, this study establishes relationships between the seismic damage failure state, performance level, repairability, critical displacement angle, and critical damage indicators for composite columns. Corresponding the critical displacement angles at each performance level are determined as 1/170, 1/106, 1/50, 1/35, and 1/30. The conclusions of this study provide a reference for assessing the damage performance of this type of composite column under seismic loading.