An information transmission method, comprising: receiving (204, 301) downlink control information sent by a network device, wherein the downlink control information comprises a resource allocation field, and the resource allocation field is used to indicate one or more resource blocks or a subcarrier resource allocated to a terminal device; and when the resource allocation field is used to indicate the allocated one or more resource blocks, the resource allocation field comprises ⌈ log 2 ⌊ N RB UL 6 ⌋ ⌉ high-order bits and M low-order bits, the ⌈ log 2 ⌊ N RB UL 6 ⌋ ⌉ high-order bits indicate an index of a narrowband, the M low-order bits indicate resource allocation in the narrowband, a quantity of resource blocks indicated by the resource allocation field is greater than or equal to 1, M is a positive integer, and N RB UL represents a quantity of resource blocks comprised in uplink bandwidth; or when the resource allocation field is used to indicate the allocated subcarrier resource, the resource allocation field comprises ⌈ log 2 ⌊ N RB UL 6 ⌋ ⌉ high-order bits and L low-order bits, the ⌈ log 2 ⌊ N RB UL 6 ⌋ ⌉ high-order bits indicate an index of a narrowband, the L low-order bits indicate subcarrier resource allocation in K resource blocks, a quantity of subcarriers indicated by the resource allocation field is less than 12, L is a positive integer, and K is a positive integer; and determining (205, 302) an allocated resource based on the downlink control information, and sending (206, 302) information on the allocated resource; wherein the terminal device is at a coverage enhancement level 0 or a coverage enhancement level 1, or in a coverage enhancement mode A; the downlink control information further comprises a first field, and a size of the first field is 2 bits; the first field has three bit states respectively indicating three different quantities of resource units, and/or the first field has one bit state indicating that the resource allocation field is used to indicate the allocated one or more resource blocks; and when the first field indicates a quantity of resource units, the resource allocation field indicates the subcarrier resource allocation. receiving (204, 301) downlink control information sent by a network device, wherein the downlink control information comprises a resource allocation field, and the resource allocation field is used to indicate one or more resource blocks or a subcarrier resource allocated to a terminal device; and when the resource allocation field is used to indicate the allocated one or more resource blocks, the resource allocation field comprises ⌈ log 2 ⌊ N RB UL 6 ⌋ ⌉ high-order bits and M low-order bits, the ⌈ log 2 ⌊ N RB UL 6 ⌋ ⌉ high-order bits indicate an index of a narrowband, the M low-order bits indicate resource allocation in the narrowband, a quantity of resource blocks indicated by the resource allocation field is greater than or equal to 1, M is a positive integer, and N RB UL represents a quantity of resource blocks comprised in uplink bandwidth; or when the resource allocation field is used to indicate the allocated subcarrier resource, the resource allocation field comprises ⌈ log 2 ⌊ N RB UL 6 ⌋ ⌉ high-order bits and L low-order bits, the ⌈ log 2 ⌊ N RB UL 6 ⌋ ⌉ high-order bits indicate an index of a narrowband, the L low-order bits indicate subcarrier resource allocation in K resource blocks, a quantity of subcarriers indicated by the resource allocation field is less than 12, L is a positive integer, and K is a positive integer; and determining (205, 302) an allocated resource based on the downlink control information, and sending (206, 302) information on the allocated resource; wherein the terminal device is at a coverage enhancement level 0 or a coverage enhancement level 1, or in a coverage enhancement mode A; the downlink control information further comprises a first field, and a size of the first field is 2 bits; the first field has three bit states respectively indicating three different quantities of resource units, and/or the first field has one bit state indicating that the resource allocation field is used to indicate the allocated one or more resource blocks; and when the first field indicates a quantity of resource units, the resource allocation field indicates the subcarrier resource allocation.