Wireless local area network access method, device and system

The invention relates to an accessing method of a wireless local area network, comprising the following steps: generating the random number to perform the access authentication of STA and AP; calculating PMKID using the random number and establishing a safety conjunction PMKSA; STA accessing network using established PMKSA. The said invention also relates to a terminal of wireless local area network, an access point and a wireless local area network system. The system cost is effectively prevented from rising and the existing system is freely compatible.