The development of the computer network and wide application of Internet have accelerated the process of enterprises and social informalities

but at the same time they have brought a lot of network security problems. So

according to the network application inside enterprises and the security problems existing in network

the paper presents some methods such as using the tri-layer switch and VLAN technology to realize user access control

using corresponding firewalls on the different levels of the network model to realize the isolation between interior and exterior network. Moreover

data transmission by encryption and identity authentication by digital signature were realized by using IDE-C++ Builder and SQL database technology

and the log management sub-system as well as database backup sub-system were constructed. The network security is complicated system engineering

so many kinds of security policy is needed to be use in concert with each other

and multilayer multidimensional precaution architecture of network security needed to be established also in order to improve the security of networks as a whole.