The invention provides a wireless channel idle detection method based on IEEE802.11n, comprising the following steps: dividing the received signal into an upper sideband signal and a lower sideband signal respectively with the bandwidth of 20 MHz if the bandwidth of the received signal is 40 MHz; performing carrier sense on the upper sideband signal and the lower sideband signal simultaneously; performing the energy detection on the upper sideband signal and the lower sideband signal simultaneously; and giving the idle instructions of the upper sideband channel and the lower sideband channel if an effective carrier signal is sensed in the set carrier sense time window, otherwise respectively giving the status instructions of the upper sideband channel and the lower sideband channel according to the result of the carrier sense and the result of the energy detection. The method of the invention effectively realizes the multiple access and the conflict avoidance, and ensures the compatibility of the 802.11n to the protocols of other versions.