The present invention is directed to a wireless communication system. Specifically, the present invention is directed to a method of controlling network access and an apparatus therefore, wherein the method comprises: receiving a first field for indicating network overload situation and a second field for indicating a network access priority; and receiving at least one of a N-bit field for indicating a first back-off window and a M-bit field for indicating a second back-off window, wherein if a configured priority is equal to or higher than the network access priority, a random access (RA) procedure is performed using the first back-off window, wherein if the configured priority is lower than the network access priority, the RA procedure is selectively barred or performed using at least one of the first back-off window and the second back-off window.