A nominal packet padding value indication method, comprising: generating, by a first device, a physical layer protocol data unit, PPDU, wherein the PPDU comprises a physical layer packet extension thresholds present subfield and a physical layer packet extension thresholds field, a value of the physical layer packet extension thresholds present subfield is 1, the physical layer packet extension thresholds field comprises a resource unit, RU, index bitmask subfield, a number of spatial streams, NSS, subfield, and a physical layer packet extension thresholds information field, wherein the physical layer packet extension thresholds information field comprises a plurality of packet extension threshold subfield sets, each packet extension threshold subfield set indicates a modulation threshold corresponding to an NSS of n and an RU or a multiple resource unit, MRU, with an index b, and the modulation threshold is used to determine a nominal packet padding value to be used, wherein a value range of n is a subset of [1,..., N], N is an integer greater than 1, a value range of b is a subset of [0,..., M], M is an integer greater than 0, and a value of a bit in the RU index bitmask subfield corresponding to an RU or MRU with an index y is 0, the value range of b does not comprise y; and in a packet extension threshold subfield set, the value of the bit in the RU index bitmask subfield corresponding to the RU or MRU with the index y is 0 indicates that a modulation threshold corresponding to the NSS of n and the RU or MRU with the index y is same with a modulation threshold corresponding to an NSS of n and an RU or MRU with an index m1, wherein m1 is a largest index in indexes that correspond to a bit being 1 in the RU index bitmask subfield and that are less than y; and sending, by the first device, the PPDU. generating, by a first device, a physical layer protocol data unit, PPDU, wherein the PPDU comprises a physical layer packet extension thresholds present subfield and a physical layer packet extension thresholds field, a value of the physical layer packet extension thresholds present subfield is 1, the physical layer packet extension thresholds field comprises a resource unit, RU, index bitmask subfield, a number of spatial streams, NSS, subfield, and a physical layer packet extension thresholds information field, wherein the physical layer packet extension thresholds information field comprises a plurality of packet extension threshold subfield sets, each packet extension threshold subfield set indicates a modulation threshold corresponding to an NSS of n and an RU or a multiple resource unit, MRU, with an index b, and the modulation threshold is used to determine a nominal packet padding value to be used, wherein a value range of n is a subset of [1,..., N], N is an integer greater than 1, a value range of b is a subset of [0,..., M], M is an integer greater than 0, and a value of a bit in the RU index bitmask subfield corresponding to an RU or MRU with an index y is 0, the value range of b does not comprise y; and in a packet extension threshold subfield set, the value of the bit in the RU index bitmask subfield corresponding to the RU or MRU with the index y is 0 indicates that a modulation threshold corresponding to the NSS of n and the RU or MRU with the index y is same with a modulation threshold corresponding to an NSS of n and an RU or MRU with an index m1, wherein m1 is a largest index in indexes that correspond to a bit being 1 in the RU index bitmask subfield and that are less than y; and sending, by the first device, the PPDU.