A motor-operated penetrometer with novel structure and constant-velocity (30mm/s) was developed. The major innovation was to employ ball screw as transmission component of penetration force so that the higher control accuracy and operating efficiency could be simultaneously obtained. Moreover, a microcomputer-based controller associated with GPS and PDA was designed to coordinate the soil penetration resistance and the depth measurements at real-time and to monitor the operating status of the penetrometer. By using of the available hardware and software provided by PDA, the data capacity and the processing ability of field information was significantly improved.