This paper introduces the principle of the DNS, and uses GNS3 and VirtualBox to build an experimental environment for the domain name system of private service. It also designs the experimental scheme of the DNS, and configures the WWW server and E-mail server. Using Wireshark is used to capture and analyze packets, the principle of the recursive query and iterative query is then introduced, the effects of the SOA record, NS record, A record, MX record and the principle of spoofing DNS are all explained, and the DNS work process is verified. The experiment lets the students better understand the working principle of DNS from both theory and practice. It enhances the practical ability and the comprehensive application ability of students.