The invention discloses an internet protocol (IP) address translation method, an internet protocol (IP) address translation device, network address translation equipment and an authentication system, and relates to the technical field of IP networks. The method comprises the following steps of: respectively sorting IP addresses in a private IP address pool and a public IP address pool; acquiring public address multiplex ratio according to a port range and the size of a port block; and determining the position of a public IP address to be allocated in the public IP address pool according to the position of a private IP address in the private IP address pool and the public address multiplex ratio, and thus determining the public IP address to be allocated and the corresponding port block. According to the invention, a fixed mapping idea is provided, and a quick address mapping method and a quick address mapping device are provided, so the mapping table generating speed of the equipment or the system is greatly increased, and the interaction process of the network address translation equipment and the authentication system is eliminated. The invention has the advantages of operability and practicability.