Abstract: The influence of low temperature treatment on the carbide precipitation in 3Cr2MoCoWV hot work die steel was studied by optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicate that after austempering Fe3C and ε-carbide precipitations could be observed in microstructure of low bainite of steel matrix. There were an abundance of twin-martensites on which fine carbide dispersed, appearing in the microstructure of specimen after the subsequent low temperature treatment. After temper treatment, a large amount of MC and M2C ε-carbides precipitation dispersedly distributed on the bainitic ferrite laths. Meanwhile, Fe3C forming in the austempering process decomposed and formed the more stable acicular M2C carbide, which maintained the same orientation of the ferrite matrix.