动态DNS（英语：Dynamic DNS，简称DDNS）是域名系统（DNS）中的一种自动更新名称服务器（Name server）内容的技术。根据互联网的域名订立规则，域名必须跟从固定的IP地址。但动态DNS系统为动态网域提供一个固定的名称服务器（Name server），透过即时更新，使外界用户能够连上动态用户的网址。

这个术语被用来描述两种不同的概念。在互联网的管理层面来说，动态DNS更新是指创建一个DNS系统，能够自动更新传统的DNS记录，而不需要手动编辑。这个机制在RFC 2136中被解释，利用TSIG机制来提供安全性。

Dynamic DNS (DDNS or DynDNS) is a method of automatically updating a name server in the Domain Name System (DNS), often in real time, with the active DDNS configuration of its configured hostnames, addresses or other information.

The term is used to describe two different concepts. The first is "dynamic DNS updating" which refers to systems that are used to update traditional DNS records without manual editing. These mechanisms are explained in RFC 2136, and use the TSIG mechanism to provide security. The second kind of dynamic DNS permits lightweight and immediate updates often using an update client, which do not use the RFC2136 standard for updating DNS records. These clients provide a persistent addressing method for devices that change their location, configuration or IP address frequently.