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Abstract: Temporary plugging and diversion fracturing (TPDF) is widely used to promote the uniform and complex distribution of multi-clustered hydraulic fractures (HFs) in a horizontal well of the unconventional formations. However, the migration behavior of temporary plugging agent (TPA), as a function of the concentration and particle size of TPA and cluster-perforation numbers, etc., determining the effectiveness of this technique, remains unclear. Therefore, this study conducted innovatively a series of TPDF simulation experiments on transparent polymethyl methacrylate (PMMA) specimens (cubic block of 30 cm × 30 cm × 30 cm) to explore visually the migration behavior of TPA in multi-clustered HFs in a horizontal well. A laboratory hydraulic sandblasting perforation completion technique was implemented to simulate the multi-cluster perforations. All the distributions of wellbore, perforations, HFs, and TPA can be seen clearly inside the PMMA specimen post the experiment. The results show that there are four characteristic plugging positions for the TPA: mouth of HF, middle of HF, tip of HF, and the intersection of HFs. Small particle size TPA tends to migrate to the fracture tip for plugging, while large particle size TPA tends to plug at the fracture mouth. The migration of the TPA is influenced obviously by the morphology of the fracture wall. A smooth fracture wall is conducive to the migration of the TPA to the far end of HFs, but not conducive to generating the plugging zone and HF diversion. In contrast, a "leaf vein" fracture of rough wall is conducive to generating the plugging layer and the diversion of HFs, but not conducive to the migration of the TPA to the far end of HFs. The migration ability of TPA in a "shell" pattern is intermediate between the two above cases. Increasing TPA concentration can encourage TPA to migrate more quickly to the characteristic plugging position, and thereby to promote the creation of effective plugging and subsequently the multi-stage diversion of the HFs. Nevertheless, excessive concentration may cause the TPA to settle prematurely, affecting the propagation of the HFs to the far end. Increasing the number of clusters to a certain extent can encourage TPA to migrate into the HFs and form plugging, and promote the diversion. An evaluation system for the migration ability of granular TPA has been established, and it was calculated that when there is no plugging expectation target, the comprehensive migration ability of small particle size TPA is stronger than that of large particle size TPA. This research provides theoretical foundation for the optimization of temporary plugging parameters.