Gesture communication is one of the most general communication methods in the world, with the obvious advantage of exchanging information without worrying about the borderline of different languages. Therefore, establishing a cost-effective way of capturing and understanding human gestures has long been a popular research topic regarding human-machine interaction, particularly in emerging scenarios such as smart cities, etc. In this paper, we propose a system based on a commercially available mmWave radar to recognize digits represented by the travel path of the human hand using a specially designed convolutional neural network (CNN) algorithm. We illustrate the proposed system is capable of recording the path of the moving hand in real-time at the cost of 1 transmitter, 2 receivers, and 2.78 GHz bandwidth from the mmWave radar. Our experimental results show that an average prediction accuracy of 98.8% is achieved in a validation test based on a 7:3 ratio split from existing dataset and an average prediction accuracy of 95.3% in generalization test using fresh data.