The evolution of the microstructure and the dimension of as-molded parts were studied on the basis of the thermogravimetric analysis of wax-based MIM binder. The results show that the binder removal speeds are different in different temperature ranges during binder removal process. The evolution of the microstructure of as-molded parts during binder removal process clearly showed the initiation and formation of connected pore structure , which is the removal chan-nel of the binder. The as-molded parts almost continuously shrank through binder removal process, except an expansion stage during 320～440℃, which is the dissolution expansion effect due to the dissolution of VPW in the polymer melt.