A multi-band indication method, comprising: generating, by a first communications device, a first frame, wherein the first frame comprises a first operating class field, and when a basic service set, BSS established by the first communications device simultaneously works in a first band and a second band, the first operating class field is used to indicate a starting frequency of the second band, wherein the first band is a band that comprises a primary channel, and the second band is a band that does not comprise the primary channel; and sending, by the first communications device, the first frame, wherein the first frame further comprises N channel center frequency segment fields and a multi-band aggregation mode field, and a value of N is a positive integer greater than or equal to 2; the multi-band aggregation mode field is used to indicate a band to which a frequency segment corresponding to at least one channel center frequency segment field in the N channel center frequency segment fields belongs; and the N channel center frequency segment fields are used to indicate N frequency segments in which the BSS works, wherein when N is equal to 4, the N channel center frequency segment fields are a first channel center frequency segment field, a second channel center frequency segment field, a third channel center frequency segment field, and a fourth channel center frequency segment field; the multi-band aggregation mode field is used to indicate bands to which frequency segments corresponding to the second channel center frequency segment field, the third channel center frequency segment field, and the fourth channel center frequency segment field belong; and the first channel center frequency segment field, the second channel center frequency segment field, the third channel center frequency segment field, and the fourth channel center frequency segment field are used to indicate four frequency segments in which the BSS works. generating, by a first communications device, a first frame, wherein the first frame comprises a first operating class field, and when a basic service set, BSS established by the first communications device simultaneously works in a first band and a second band, the first operating class field is used to indicate a starting frequency of the second band, wherein the first band is a band that comprises a primary channel, and the second band is a band that does not comprise the primary channel; and sending, by the first communications device, the first frame, wherein the first frame further comprises N channel center frequency segment fields and a multi-band aggregation mode field, and a value of N is a positive integer greater than or equal to 2; the multi-band aggregation mode field is used to indicate a band to which a frequency segment corresponding to at least one channel center frequency segment field in the N channel center frequency segment fields belongs; and the N channel center frequency segment fields are used to indicate N frequency segments in which the BSS works, wherein when N is equal to 4, the N channel center frequency segment fields are a first channel center frequency segment field, a second channel center frequency segment field, a third channel center frequency segment field, and a fourth channel center frequency segment field; the multi-band aggregation mode field is used to indicate bands to which frequency segments corresponding to the second channel center frequency segment field, the third channel center frequency segment field, and the fourth channel center frequency segment field belong; and the first channel center frequency segment field, the second channel center frequency segment field, the third channel center frequency segment field, and the fourth channel center frequency segment field are used to indicate four frequency segments in which the BSS works.