To achieve the goal of preparing an in situ microfibril composite (MFC), multiple strong shear flows were imposed on the melt of high-density polyethylene (HDPE)/polystyrene (PS). During vibration injection molding (VIM), both phase morphology and crystalline structure show big differences from the common injection molding (CIM) samples. The PS phase would deform into ultrafine microfibrils and then absorb the HDPE matrix to form a shish kebab super crystalline structure. The morphology analysis shows that when PS content increases, the size and morphology would change correspondingly. When PS content reaches a certain level, it would impair the mechanical performance. This work also analyzes the relationship between blending ratio and crystalline structure and explains the difference. These results provide valuable insight into immiscible polymer systems under a shearing field and have future industrial prospects.