A data transmission method performed by a base station, the method comprising: o determining a transmission policy, wherein the transmission policy is used for contention-based uplink data transmission or non-contention based uplink data transmission (301, 501, 511), o if a remaining resource capacity of a physical downlink control channel, PDCCH, is greater than or equal to a first threshold: the determined transmission policy is a first transmission indication, wherein the first transmission indication is used to indicate the non-contention based uplink data transmission; o if the remaining resource capacity of the PDCCH is less than a second threshold: the determined transmission policy is a second transmission indication, wherein the second transmission indication is used to indicate the contention-based uplink data transmission; o if the remaining resource capacity of the PDCCH is greater than or equal to the second threshold and is less than the first threshold: the determined transmission policy is a transmission parameter, wherein the transmission parameter is used at a terminal to determine the contention-based uplink data transmission or the non-contention based uplink data transmission, and the transmission parameter is an uplink channel quality between the terminal and the base station, wherein the second threshold is less than the first threshold; and o sending the determined transmission policy to the terminal (302, 502, 512). o determining a transmission policy, wherein the transmission policy is used for contention-based uplink data transmission or non-contention based uplink data transmission (301, 501, 511), o if a remaining resource capacity of a physical downlink control channel, PDCCH, is greater than or equal to a first threshold: the determined transmission policy is a first transmission indication, wherein the first transmission indication is used to indicate the non-contention based uplink data transmission; o if the remaining resource capacity of the PDCCH is less than a second threshold: the determined transmission policy is a second transmission indication, wherein the second transmission indication is used to indicate the contention-based uplink data transmission; o if the remaining resource capacity of the PDCCH is greater than or equal to the second threshold and is less than the first threshold: the determined transmission policy is a transmission parameter, wherein the transmission parameter is used at a terminal to determine the contention-based uplink data transmission or the non-contention based uplink data transmission, and the transmission parameter is an uplink channel quality between the terminal and the base station, wherein the second threshold is less than the first threshold; and o if a remaining resource capacity of a physical downlink control channel, PDCCH, is greater than or equal to a first threshold: the determined transmission policy is a first transmission indication, wherein the first transmission indication is used to indicate the non-contention based uplink data transmission; o if the remaining resource capacity of the PDCCH is less than a second threshold: the determined transmission policy is a second transmission indication, wherein the second transmission indication is used to indicate the contention-based uplink data transmission; o if the remaining resource capacity of the PDCCH is greater than or equal to the second threshold and is less than the first threshold: the determined transmission policy is a transmission parameter, wherein the transmission parameter is used at a terminal to determine the contention-based uplink data transmission or the non-contention based uplink data transmission, and the transmission parameter is an uplink channel quality between the terminal and the base station, wherein the second threshold is less than the first threshold; and o sending the determined transmission policy to the terminal (302, 502, 512).