A method used for coordinated transmission in a wireless fidelity, WiFi, system, comprising: receiving (S210), by an access point, AP, an uplink preamble training sequence transmitted by a station, STA; determining (S220), by the AP, uplink quality information according to the uplink preamble training sequence; and transmitting (S230), by the AP, the uplink quality information to a server, to enable the server to determine a downlink coordinated transmission set according to the uplink quality information; receiving (S240), by the AP, a downlink coordinated transmission set notification message transmitted by the server to the downlink coordinated transmission set; transmitting (S250), by the AP, a null data packet, NDP, to the STA according to the downlink coordinated transmission set notification message, wherein the NDP carries information indicating that a feedback type is coordinated transmission, to enable the STA to measure downlink channel state information, CSI; receiving (S260), by the AP, downlink CSI corresponding to the downlink coordinated transmission set transmitted by the STA; transmitting (S270), by the AP, the downlink CSI corresponding to the downlink coordinated transmission set to the server, to enable the server to determine coordinated information according to the downlink CSI corresponding to the downlink coordinated transmission set; receiving (S280), by the AP, the coordinated information transmitted by the server; and performing (S290), by the AP, downlink coordinated transmission to the STA according to the coordinated information; wherein the uplink preamble training sequence comprises a newly-added precoded symbol, and the newly-added precoded symbol is used for CSI measurement. receiving (S210), by an access point, AP, an uplink preamble training sequence transmitted by a station, STA; determining (S220), by the AP, uplink quality information according to the uplink preamble training sequence; and transmitting (S230), by the AP, the uplink quality information to a server, to enable the server to determine a downlink coordinated transmission set according to the uplink quality information; receiving (S240), by the AP, a downlink coordinated transmission set notification message transmitted by the server to the downlink coordinated transmission set; transmitting (S250), by the AP, a null data packet, NDP, to the STA according to the downlink coordinated transmission set notification message, wherein the NDP carries information indicating that a feedback type is coordinated transmission, to enable the STA to measure downlink channel state information, CSI; receiving (S260), by the AP, downlink CSI corresponding to the downlink coordinated transmission set transmitted by the STA; transmitting (S270), by the AP, the downlink CSI corresponding to the downlink coordinated transmission set to the server, to enable the server to determine coordinated information according to the downlink CSI corresponding to the downlink coordinated transmission set; receiving (S280), by the AP, the coordinated information transmitted by the server; and performing (S290), by the AP, downlink coordinated transmission to the STA according to the coordinated information; wherein the uplink preamble training sequence comprises a newly-added precoded symbol, and the newly-added precoded symbol is used for CSI measurement. <EOS>