An information transmission method, comprising: determining a maximum orthogonal frequency division multiplexing OFDM symbol quantity of a frequency band used for downlink transmission, wherein the maximum OFDM symbol quantity of the frequency band is a maximum value of maximum OFDM symbol quantities of all subbands of the frequency band; determining, when the maximum OFDM symbol quantity of the subband to which a user equipment belongs is less than the maximum OFDM symbol quantity of the frequency band, according to a value relationship between a maximum OFDM symbol quantity of a subband to which the user equipment belongs and the maximum OFDM symbol quantity of the frequency band, additional long training field instruction information used to instruct whether to send an additional long training field to the user equipment; wherein the maximum OFDM symbol quantity of the subband to which the user equipment belongs is a maximum value of a quantity of OFDM symbols required for sending, on the subband to which the user equipment belongs, a preamble field and a data field to the user equipment, wherein the preamble field includes at least an initial long training field; determining a target quantity of OFDM symbols used for sending the additional long training field to the user equipment, wherein the target quantity of OFDM symbols is less than or equal to a difference between the maximum OFDM symbol quantity of the frequency band and the maximum OFDM symbol quantity of the subband to which the user equipment belongs; wherein the additional long training field instruction information comprises the target quantity of OFDM symbols and sending an indication message to the user equipment, wherein the indication message comprises the additional long training field instruction information and sending the additional long training field and an initial long training field to the user equipment according to the additional long training field instruction information. determining a maximum orthogonal frequency division multiplexing OFDM symbol quantity of a frequency band used for downlink transmission, wherein the maximum OFDM symbol quantity of the frequency band is a maximum value of maximum OFDM symbol quantities of all subbands of the frequency band; determining, when the maximum OFDM symbol quantity of the subband to which a user equipment belongs is less than the maximum OFDM symbol quantity of the frequency band, according to a value relationship between a maximum OFDM symbol quantity of a subband to which the user equipment belongs and the maximum OFDM symbol quantity of the frequency band, additional long training field instruction information used to instruct whether to send an additional long training field to the user equipment; wherein the maximum OFDM symbol quantity of the subband to which the user equipment belongs is a maximum value of a quantity of OFDM symbols required for sending, on the subband to which the user equipment belongs, a preamble field and a data field to the user equipment, wherein the preamble field includes at least an initial long training field; determining a target quantity of OFDM symbols used for sending the additional long training field to the user equipment, wherein the target quantity of OFDM symbols is less than or equal to a difference between the maximum OFDM symbol quantity of the frequency band and the maximum OFDM symbol quantity of the subband to which the user equipment belongs; wherein the additional long training field instruction information comprises the target quantity of OFDM symbols and sending an indication message to the user equipment, wherein the indication message comprises the additional long training field instruction information and sending the additional long training field and an initial long training field to the user equipment according to the additional long training field instruction information.