Eco-friendly concrete becomes research hotspots since concrete production emits 8–10% of the total anthropogenic CO2 emissions worldwide. Industry solid waste modification exhibits great potentials on mitigating aggregates depletion and carbon emissions. Coal gangue aggregate (CGA) coated by silica fume manually (CGACM) and in a desiccator (CGACD) are utilised to optimize the 3D printing concrete. Specimens were printed by a 3D printing robotic arm with a 25 mm-diameter nozzle. The compressive strength of CGACM and CGACD increases by 49% and 44% than non-activated series. For splitting tensile strength, the figures are 43% and 36%. The density of activation series decreases over 16% compared with standard sand. However, both surface pretreated methods make negative effects on structure compactness. From the SEM, SiO2 particles filles defects of aggregates, resulting in a denser internal structure and promoting secondary hydration reaction. However, excessive SiO2 particles agglomerated on CGA leads to the lubricant film among particles. These results expand recycle methods for CG and promotes 3D printing technology application on mine.