A high–contrast X–ray computed tomography (XCT) applied to the ternary polymer blends of poly(methyl methacrylate) (PMMA), polypropylene (PP) and polyamide 12 (PA12), we investigated micro–structure three–dimensional (3D) images of blends with gradually increasing of molecular weight (Mw) of PMMA. The 1:1:1 mixture of PMMA/PP/PA12 were prepared by mixing on an internal mixer at 200 °C, then annealing at 200 °C under compressor of 5 MPa in order to restore the crystalline structure of polymer blends. After that, blends were compressed molding and cooled by water. Finally, they were stored in the vacuum oven at the same annealing temperature before taking XCT and then rendering to 3D images. Changing various methods of annealing time, we could observe vary 3D internal structure clearly of these blends. We also conclude the effect between Mw of PMMA and the morphologies of these ternary polymer blends.