In this paper, the injection molding process parameter determination method based on computer-aided engineering (CAE) and orthogonal experiments is adopted to study the microstructural cavity of the modified glass-fiber-enhanced polybutylene terephthalate (PBT) subjected to severe short shots under conventional injection molding conditions. Cavity pressure is accurately controlled by monitoring the cavity pressure curve. At the same time, the parameters of injection molding technology were optimized. The effect of the supersonic vibration field on the flow behavior of the glass-fiber-enhanced PBT microstructural injection molding melt was analyzed. The effects of the conventional forming process and supersonic vibration on the quality and properties of injection molding were also examined. The results suggest that the supersonic vibration field could not only lower the viscosity of the polymer melt and increase its fluidity but also enhance the mechanical properties of the products, reduce buckling deformation, and improve the appearance and filling quality of the products.