A method for indicating a transmission opportunity (TXOP) duration in a wireless communication system includes generating, by a TXOP holder, a physical layer protocol data unit (PPDU). The PPDU includes a High Efficiency Signal field A (HE-SIGA), and the HE-SIGA includes a TXOP duration field. The TXOP duration field is used to indicate to other stations a remaining time for using a channel by a station. The TXOP duration field includes a first part which indicates a granularity used, and a second part which indicates the TXOP duration using the granularity indicated by the first part. The TXOP holder sends the generated PPDU.