Nowadays

the network address is getting exhausted.How to make more efficient use of limited IP address has become the urgent problem which the telecom operators need to solve.The core idea of Network Address Translation（NAT）is letting a small number of external addresses to represent a large number of internal addresses.This paper uses the design ideas of distributed software and the separation of forward and control to achieve the layering and modularization of NAT function.The implementation of NAT function includes static NAT

dynamic NAT and Port Address Translation（PAT）.Compared with the centralized software design

the main features of this paper include:the separation of forward and control makes NAT more efficiency;the independent management module makes the internal management more convenient and more operational;the distributed multi-process design makes the module has higher protability.