Security mechanism detection is not only an important content of vulnerabilities evaluation but also the foundation of key strength test for wireless local area network(WLAN). This paper analyzes the specifications of WLAN security mechanisms and points out the defects in design of security mechanisms detection algorithm based on the standards. By capturing and analyzing a large number of Beacon frames from different vendor’s access points(APs),we summarize the relevant fields and information elements in a Beacon frame,and present their values or status when an AP is set to every specific security mechanism. A detection algorithm of WLAN security mechanisms is proposed based on the experimental study result and the pseudo code of a reference implementation for the algorithm is designed. The validity of the algorithm is illustrated by examples,which shows it can detect every WLAN security mechanism accurately. Security mechanism detection is not only an important content of vulnerabilities evaluation but also the foundation of key strength test for wireless local area network (WLAN). This paper analyzes the specifications of WLAN security mechanisms and points out the defects in design of security mechanisms detection algorithm based on the standards. By capturing and analyzing a large number of Beacon frames from different vendor’s access points (APs), we summarize the relevant fields and information elements in a Beacon frame, and present their values ​​or status when an AP is set to every specific security mechanism. A detection algorithm of WLAN security mechanisms is proposed based on the experimental study result and the pseudo code of a reference implementation for the algorithm is designed. The validity of the algorithm is illustrated by examples, which shows it can detect every WLAN security mechanism accurately.