Abstract: The access control of local area network is a common security problem which involved the resource protection of local area network. In this paper, a project of access control of local area network based on ARP protocol is presented. It can be used to detect and refuse the illegal computers that try to log on and access the local area network by capturing and analyzing the network packets. On the other hand, through the authentication of the local area network server and based on the ARP buffer principle, it can be also used to control the access between the legal computers of the local area network. So that it is an effective way to protect the resource of local area network. The project is convenient and useful.