Since animal meat has been a major source of protein, conventional livestock farming is ever-increasing, as the global population grows. But the livestock farming has caused serious resource and environmental issues in recent years, such as greenhouse gas emissions, land occupation, water consumption, and loss of biodiversity. Alternatively, plant protein meat (PPM) can be expected to serve as the animal meat analogue, in order to alleviate the shortage of animal meat, resource consumption, and environmental pollution. The primary processing techniques for PPM currently include extrusion, spinning, shearing, and 3D printing. Specifically, the emerging 3D printing has been successfully applied to PPM production in the food industry, thus enabling customization of nutritional content, shape, texture, and flavor. Previous studies of 3D-printed PPM have focused primarily on material formulations, process parameters, or nozzle structures in conventional 3D printing. Among them, ultrasonic vibration has been used to print highly viscous fluid materials in protein extraction, gelation, and food processing. Better performance has also been achieved to mitigate the clogging caused by small nozzle diameters or high material viscosity. However, it is still lacking in the application of ultrasonic vibration for the high quality of 3D-printed PPM. In this study, ultrasonic vibration was introduced to improve the quality of 3D-printed PPM. A systematic analysis was made to explore the mechanism of ultrasonic vibration on plant proteins. Rheological property tests and numerical simulations of 3D printing nozzles were then carried out to investigate the effect of ultrasonic vibration on the gelation of plant proteins. A novel ultrasonic vibration-assisted 3D printing system was developed for PPM using single-nozzle 3D printing. A series of experiments were conducted to clarify the influence of ultrasonic vibration on the quality of 3D-printed PPM. The numerical simulation results demonstrated there was a cyclic variation in the fluid velocity inside the printing nozzle, with the trend of increasing, decreasing, and then increasing for the uniform mixing of protein molecules. Additionally, the shear rate within the nozzle exhibited repetitive fluctuations with decreasing and then increasing, where relatively high shear rates were observed on both the surface and cross-sections of the fluid. A high-shear environment was provided for the stepwise depolymerization of protein molecules during printing. The internal fluid pressure within the nozzle also showed a cyclic variation in the decreasing and then increasing. The lowest pressure value was still higher than that in the absence of ultrasonic vibration. This fluctuation of pressure greatly contributed to the necessary conditions for the depolymerization of protein molecules. Thus, the ultrasonic vibration supplied the higher shear and pressure to the plant proteins during 3D printing. The gelation process was promoted to ultimately improve the molding quality of 3D-printed PPM products. Experimental results revealed that the printed products exhibited decreased hardness, comparable elasticity, and chewiness after ultrasonic vibration, compared with conventional 3D printing. In terms of the stability of hardness, elasticity, and chewiness, the fluctuations in these quality parameters were lower than those in the samples printed without ultrasonic vibration. Specifically, the stability of hardness, elasticity, and chewiness increased by 27.75%, 83.14%, and 59.30%, respectively, indicating a more consistent quality for the samples printed with ultrasonic vibration. The ultrasonic vibration was incorporated into the 3D printing of PPM for the stability of quality attributes. The finding can also provide valuable insights into producing high-quality plant-based protein meat using 3D printing.