Ultrasound can non-invasively detect muscle deformations, which has great potential applications in prosthetic hand control. This research developed a miniaturized ultrasound device that could be integrated into a prosthetic hand socket. This compact system included four A-mode ultrasound transducers, a signal processing module, and a prosthetic hand control module. The size of the ultrasound system was 65 * 75 * 25 mm, weighing only 85 g. For the first time, we integrated the ultrasound system into a prosthetic hand socket to evaluate its performance in practical prosthetic hand control. We designed an experiment to perform six commonly used gestures, and the classification accuracy was 95.33% +/- 7.26% for a participant. These experimental results demonstrated the efficacy of the designed prosthetic system based on the miniaturized A-mode ultrasound device, paving the way for an effective HMI system that could be widely used in prosthetic hand control.