The present invention provides a competition-based wireless network medium access control layer access method and system. The method comprises the steps that each site is in a random access state in an initial stage; determined information is monitored; whether a new site sends successfully is determined according to the determined information; if yes, all sites enter a next timeslot group, and sites in a random access state compete again in the next timeslot group; the successfully sending sites enter a deterministic access group and update time sequence information; if not, the sites compete; in the next timeslot group, sites in the deterministic access group send according to time sequence information of sending; determined information is monitored; whether sites in the deterministic access group finish sending is determined according to the determined information; if yes, sites in the random access group compete to send and enter the deterministic access group; if not, sites in the deterministic access group continue to send till the sites in the deterministic access group finish sending, and steps 2-10 are performed circularly till the sites in the random access group enter the deterministic access group; and the network enters a deterministic state, and all sites send in a new timeslot group according to time sequence information.