A method of controlling channel access for a mobile device in a wireless communication system includes receiving a dynamic persistence level from a base station, determining a persistence value according to the dynamic persistence level and at least a one persistence coefficient stored in the mobile device, comparing the persistence value with a random number of the mobile device, and determining whether access to a channel is permitted to be accessed for sending a message from the mobile device to the base station according to a comparison result of the persistence value and with the random number.