The invention provides an adaptive determinacy back-off method of an MAC layer in a wireless distributed network. The method comprises the steps as follows: step 1, judging whether the No. (i)i(/i) site has a data package needing to transmit; continuing to execute the next step if the No. (i)i(/i) site has a data package needing to transmit, otherwise, executing back-off window value updating operation to an back-off window value in the No. (i)i(/i) site; step 2, executing first monitoring channel to judge whether a transmission channel is leisure, and executing the back-off operation if the transmission channel is leisure and executing second monitoring channel; otherwise, executing second back-off operation and returning to the second monitoring channel, wherein the second back-off operation comprises the back-off window value updating operation; step 3, executing the second monitoring channel to judge whether the transmission channel is leisure, and transmitting the data package needing to transmit out if the transmission channel is leisure, and executing the follow-up operation related to the transmission, and otherwise, returning and executing the second back-off operation. The method of the invention realizes a back-off mechanism of the determinacy, effectively avoids the collision of the data package, and effectively improves the throughput capacity and transmission success rate of a network system.