Abstract: the crack propagation behavior of brittle materials such as rock is often difficult to capture under explosive loading. Based on the theory of explosive damage, model experiments were conducted using transparent polymethyl methacrylate (PMMA) to simulate the fracture response of brittle materials. High-speed photography and CT scanning were utilized to investigate the dynamic fracture process and three-dimensional crack evolution under blast loading. In addition, 3D scanning technology was employed to reconstruct the morphology of cracks and characterize the fracture surface features. Results show that under the sustained action of multi-stage explosive energy, cracks undergo repeated initiation and propagation. Initial cracks induced by shock waves exhibit high density and a "fish scale" pattern concentrated around the blast hole. In contrast, secondary cracks driven by detonation gases present lower density and extend outward in "ear-shaped" or "dagger-shaped" forms. As the distance from the explosion center increases, the crack surface morphology transitions from rugged to microwave-like textures, with improved flatness. The elevation variance of the fracture surface decreases from 0.796 to 0.586, while the maximum height reduces from 3.2 mm to 2.8 mm, representing a 12.5% reduction. Moreover, the failure mode of the material shifts from compressive-shear to tensile failure with increasing distance, accompanied by a decline in both the fractal dimension of crack distribution and the overall damage degree of the model.