In order to obtain the projections with short cracks, a novel subvoxel model is proposed for short crack simulation. Short cracks are modeled in subvoxel space. Giving an initial subvoxel as an initial cracking point, a short crack is simulated according to the random growing mode. If there are multiple initial cracking points, multi-cracks can be simulated easily, and short cracks are visualized using CT. Limited by the resolution of real CT system, it is not possible to detect individual short crack but a group of them. By pre-processing the reconstructed images, new images are obtained, which are very close to actual conditions. The differences between the reconstructed images without short cracks and the images with short cracks are analyzed. Experiment results proved that it is feasible to detect short crack behavior by analyzing the grey level variance of the images.