With the growth of decentralized network users, preserving privacy becomes a critical issue in this open community. Kad-based network, as a typical decentralized system, has been widely used nowadays. However, there is not enough research to achieve anonymity on it. In this paper, we propose an anonymous protocol based on Kad network, named Anonymous Kad (A-Kad), which achieves complete privacy and security for file providers and requesters. A-Kad has the desired property of anonymity and still keeps high efficiency in publishing and querying phases. To achieve anonymity, we establish two anonymous channels which help file providers to anonymously publish file information and securely transfer files. Through these two channels, the file requester can also efficiently query and retrieve files without worrying about exposing its behavior. Moreover, we propose an anonymity degree evaluation model (ADEM) according to three different attacking capabilities and anonymity degree.