Characterization of pore structure inside grain bulks is essential for predicting the airflow resistance during grain drying, aeration, and fumigation. The 3D pore network of wheat mixtures mixed with different percentages of canola and dockage material was characterized. The characterized parameters include pore size, throat length, coordination number, airpath length, and tortuosity. The tested wheat mixtures include different combinations of clean wheat kernels mixed with 10% of canola or 5 or 10% of wheat dockage. To simulate the grain storage condition, the loaded wheat mixtures were cured by using wax at 110oC. The images of the waxed wheat mixtures were produced by using a high-resolution micro-X-ray computed tomography (XRCT) system at 50 μm/pixel resolution. The computed space distribution was based on the 3D medial axis analysis of each image stack using Dragonfly 4.1 software. The pore space was segmented using a deep-learning model with an accuracy between 90.1-98.0%. A watershed-based image algorithm was used to generate the pore network from the segmented pore space. The pore structure parameters were extracted from the pore network of each wheat mixture. Most pores were classified as mesopores (>99%) in a range from 62.5 to 4000 μm, with less than 1% classified as micropores (1-62.5 µm). The mean pore size of clean bulk wheat was 648 ± 403 µm with a mean throat length of 1115 ± 611 µm. When clean wheat was mixed with 10% of canola, 5 and 10% of wheat dockage, the mean pore size was reduced by 10%, 29%, and 17%, respectively, from its original value. The addition of canola and dockage generally influenced the connectivity in the pore microstructure with changes in bulk porosity, tortuosity, airpath number, and length.