In order to investigate the effect of aging treatment on the microstructure and properties of Stellite 6B cobaltbased superalloy, different aging treatment methods were used to treat the alloy samples. The microstructure, microhardness and carbide precipitation of the samples under different aging treatments were compared and analyzed. The results showed that as the aging treatment time increased, the precipitation of carbides increased, and the carbide chains that strengthen the grain boundaries begin to precipitate on the grain boundaries. When the aging treatment parameter was 980 °C×12 h, the effect was the best. At this time, the microstructure was completely austenitized, and there was no bulk primary carbide on the matrix and the grain boundary. The precipitated M23C6 carbides were uniformly dispersed and their size was controlled at about 1 μm, and the maximum was not more than 3 μm. The crystalline carbides were broken into carbide chains, and the longest was up to 5 μm. The alloy hardness was close to HRC47.18, which can meet the hardness requirements of the extrusion die materials.