A method includes generating a preamble for a protocol version of a wireless local area network, where the preamble includes a legacy signal L-SIG field and a high efficiency signal HE-SIG field that are arranged in order, the HE-SIG field includes a first orthogonal frequency division multiplexing OFDM symbol and a second OFDM symbol that are arranged in order, and an input information bit of the first OFDM symbol is the same as that of the second OFDM symbol, and sending the preamble to a receive end device, so that the receive end device restores the preamble, and when determining that input information bits obtained after restoring the first OFDM symbol and the second OFDM symbol are the same, determines that the preamble is the preamble of the protocol version.