Abstract: Ultrafine cemented carbides with the different thickness were prepared by metal powder injection molding, using WC–10Co with the particle sizes of 0.71 μm and 0.53 μm as the raw materials and the wax-based binder system as the binders. The solvent debinding process and the influence of sample thickness on the solvent debinding were studied. The results show that, the solvent debinding is the process of diffluence and diffusion, the paraffin as the low molecular component in the binders covering the WC particles is gradually dissolved, and the macromolecule component acts as the skeleton to support, keeping the samples in the original shape. The essential form of the solvent debinding cracks is the fracture of the macromolecule component skeleton. There is a debinding critical thickness for the injection molding of the cemented carbides. Based on the experimental conditions in this paper, the critical thickness of injection molding for two kinds of raw materials with the different particle sizes is 7.5 mm and 6.5 mm, respectively.