A method is described for preparing metal ink for additive manufacturing based on photo-thermal synergistic curing, relating to functional ink technology. The ink includes 50%-95% metal powder, 1%-35% photosensitive resin, 1%-35% photosensitive monomer, 0.1%-7% photoinitiator, 0.1%-5% thermal initiator, 0.1%-5% up-conversion material, and 0%-2% auxiliary agent. The method includes adding metal ink to the ink tank of a direct ink writing 3D printer, extruding the metal ink from the nozzle under computer control to the printing specific shapes on the platform, and curing under real-time illumination of a specific light source to obtain the green body. The method includes performing high-temperature debinding treatment on the obtained green body in a specific atmosphere. The treated green body is subjected to a high-temperature and high-pressure sintering treatment in a specific atmosphere and then cooled to room temperature.