A data transmission method, comprising: determining, by a base station, a modulation and coding level; according to a system overhead size, choosing, by the base station, to determine, in a first modulation and transport block size index table, a first transport block size TBS index and a first modulation mode that are corresponding to the modulation and coding level, or to determine, in a second modulation and transport block size index table, a second TBS index and a second modulation mode that are corresponding to the modulation and coding level, wherein the second TBS index is not smaller than the first TBS index; determining, by the base station, a time-frequency resource, and determining, according to the time-frequency resource, a quantity of physical resource block pairs; selecting, by the base station in a transport block size table, a transport block size TBS corresponding to the quantity of physical resource pairs and corresponding to the determined first TBS index or second TBS index; sending, by the base station, service data to a user equipment by adopting the selected TBS and the determined modulation mode; and sending, by the base station, a system scheduling control signal to the user equipment, wherein the system scheduling control signal comprises the modulation and coding level and the time-frequency resource; wherein: the first modulation and transport block size index table is a modulation and transport block size index table in Long Term Evolution Release 8, LTE REL.8; said data transmission method characterised in that for the same modulation and coding level in both first and second tables, if the second TBS index in the second modulation and transport block size index table is larger than the first TBS index in the first modulation and transport block size index table, a modulation order of the second modulation mode corresponding to the second TBS index is lower than a modulation order of the first modulation mode corresponding to the first TBS index. determining, by a base station, a modulation and coding level; according to a system overhead size, choosing, by the base station, to determine, in a first modulation and transport block size index table, a first transport block size TBS index and a first modulation mode that are corresponding to the modulation and coding level, or to determine, in a second modulation and transport block size index table, a second TBS index and a second modulation mode that are corresponding to the modulation and coding level, wherein the second TBS index is not smaller than the first TBS index; determining, by the base station, a time-frequency resource, and determining, according to the time-frequency resource, a quantity of physical resource block pairs; selecting, by the base station in a transport block size table, a transport block size TBS corresponding to the quantity of physical resource pairs and corresponding to the determined first TBS index or second TBS index; sending, by the base station, service data to a user equipment by adopting the selected TBS and the determined modulation mode; and sending, by the base station, a system scheduling control signal to the user equipment, wherein the system scheduling control signal comprises the modulation and coding level and the time-frequency resource; wherein: the first modulation and transport block size index table is a modulation and transport block size index table in Long Term Evolution Release 8, LTE REL.8; said data transmission method characterised in that for the same modulation and coding level in both first and second tables, if the second TBS index in the second modulation and transport block size index table is larger than the first TBS index in the first modulation and transport block size index table, a modulation order of the second modulation mode corresponding to the second TBS index is lower than a modulation order of the first modulation mode corresponding to the first TBS index.