The address non-transparency of NAT (Network Address Translation) device is a great challenge for managing and monitoring the network. Now a lot of problems exist in various detection technologies for obtaining the number of NATed hosts, which can't meet the need of managing and monitoring network. This paper analyzes popular detection technologies for detecting the number of NATed hosts in detail, divides them into active algorithms and passive algorithms, summarizes the advantages and disadvantages of each algorithm, and accordingly puts forward an integrative model and system. At first end users are classified according to user states, then the system makes use of passive algorithms to determine user type, after that utilizes active algorithms to calculate the number of NATed hosts exactly. This detection system has good scalability and hierarchy and can makes a new detection algorithm integrated easily, moreover it improves the accuracy of detection and avoids normal user experience to be interrupted.