The paper analyzes the security of IEEE 802.11. Based on the discussion of IEEE 802.11 security requirement, the three security technologies-SSID (Service Set Identifier), MAC(Media Access Control), WEP(Wired Equivalent Privacy) in WLAN standard IEEE802.11 are introduced, especially the encrypting algorithm and the integrity check algorithm in WEP. The security flaws caused by RC4 algorithm, key management, initialization vector Space, CRC algorithm and authentication mechanism in WEP are analyzed mainly in this paper. At the end of the paper, some advices and strategies to these flaws are given.