Conventional freehand three-dimensional (3-D) ultrasound imaging systems cannot achieve real-time and interactive reconstruction. The overall design idea, 3-D reconstruction method, and hardware/software system structure of the developed real-time and interactive freehand 3-D ultrasound imaging system, which is called RIF-3DUSIS, is introduced in this article. The characteristics of RIF-3DUSIS are as follows: (1) acquisition, 3-D reconstruction, and interactive manipulation of the reconstructed volume model in real time during scanning process; (2) While scanning, not only displaying reconstructed volume dynamically to provide visual feedback, but also updating display of reconstructed ratio sequentially to conduct reconstruction plan quantitatively; (3) Showing instruction information before each operation step so as to instruct operator’s work. Experimental results indicate the effectiveness of real-time reconstruction and the flexibility of dynamic interaction of RIF-3DUSIS.