To expand the application scope of coal gangue. In this study,gangue aggregate is used to partially or completely replace (mass fraction of 0%,50% and 100%) nutural sand in 3D printing mortar,and the effect of gangue aggregate addition on the the rheological model,rheological properties,printability,and mechanical properties of 3D printing mortar was systematically examined. The results reveal that,the addition of coal gangue reduces the mechanical properties of 3D printing mortar,but when the coal gangue content is 100%,the compressive strength at 28 d still exceeds 30 MPa,meeting the requirements for mechanical properties. The rheological properties of 3D printing mortar mixed with gangue aggregate conform to the modified Bingham model. Both static yield stress and dynamic yield stress increase proportionally with higher gangue doping. Notably,when the gangue doping is 100%,the growth rate of time-dependent static yield stress is fast,while the growth rates of time-dependent flowability and time-dependent dynamic yield stress are slow. This indicates that the introduction of gangue significantly improves the printability of 3D printing mortar.