In order to achieve real-time monitoring of long-range targets, and obtain detailed characteristics of targets comprehensively and clearly, a dual-band high-definition image acquisition system was designed. This system applied Gigabit Ethernet as data transmission path, made use of FPGA for resolution switching, and had the auto focusing function separated in the visible and near-infrared bands. According to the requirements of monitoring mode, the image data acquired by the two detectors was set to a specific resolution, and then transferred to the host computer, on which the operations such as image storage, display and auto focusing were performed. Experiment results show that this system has achieved the functions of resolution switching and auto focusing flexibility according to the system requirements, and realized the real-time displaying of remote target video and high-definition storage both in the two bands by the Gigabit Ethernet.