The present invention provides a method and a device for interleaving processing in a WLAN system, and relates to the field of communications technologies. The method includes: obtaining, by a WLAN device, a predetermined number of identifiers of valid positions from any sub-interleaving processing contained in an interleaving processing; determining valid input positions of the interleaving processing according to the identifiers of the valid positions; transmitting data bits to be transmitted in the valid input positions, and transmitting bit 0 and/or bit 1 or no data bit in other non-valid input positions of the interleaving processing other than the valid input positions; modulating data bits transmitted in interleaving processing output positions to obtain modulation signals and mapping the modulation signals onto the corresponding data sub-carriers respectively. The present invention can be applied in interleaving processing of data bits to be transmitted.