An information transmission method, comprising: when a communications device is at a coverage enhancement level 2 or a coverage enhancement level 3, or in coverage enhancement mode B, receiving, by the communications device, a random access response, wherein the random access response comprises indication information and uplink grant information, wherein the indication information is used to indicate that a message 3 to be sent by the communications device is a first message 3 or a second message 3, wherein the first message 3 is a message 3 that does not carry user data, and the second message 3 is a message 3 that carries the user data, wherein the uplink grant information comprises first resource information, second resource information, and repetition quantity information, wherein the first resource information is used to indicate a resource used by the communications device to send the message 3 on a first narrowband in an uplink bandwidth, the repetition quantity information is used to indicate a quantity of times that the communications device is to repeatedly send the message 3, and the second resource information is used to indicate an index of the first narrowband of the communications device in the uplink bandwidth; and when the indication information indicates that the message 3 to be sent by the communications device is the first message 3, a quantity of bits of the second resource information is 2; when the indication information indicates that the message 3 to be sent by the communications device is the second message 3, a quantity of bits of the second resource information is N, wherein N is a pre-specified integer, and N is equal to 3, or N is equal to 4; and sending, by the communications device, the message 3 based on the indication information, the first resource information, the second resource information, and the repetition quantity information. when a communications device is at a coverage enhancement level 2 or a coverage enhancement level 3, or in coverage enhancement mode B, receiving, by the communications device, a random access response, wherein the random access response comprises indication information and uplink grant information, wherein the indication information is used to indicate that a message 3 to be sent by the communications device is a first message 3 or a second message 3, wherein the first message 3 is a message 3 that does not carry user data, and the second message 3 is a message 3 that carries the user data, wherein the uplink grant information comprises first resource information, second resource information, and repetition quantity information, wherein the first resource information is used to indicate a resource used by the communications device to send the message 3 on a first narrowband in an uplink bandwidth, the repetition quantity information is used to indicate a quantity of times that the communications device is to repeatedly send the message 3, and the second resource information is used to indicate an index of the first narrowband of the communications device in the uplink bandwidth; and when the indication information indicates that the message 3 to be sent by the communications device is the first message 3, a quantity of bits of the second resource information is 2; when the indication information indicates that the message 3 to be sent by the communications device is the second message 3, a quantity of bits of the second resource information is N, wherein N is a pre-specified integer, and N is equal to 3, or N is equal to 4; and sending, by the communications device, the message 3 based on the indication information, the first resource information, the second resource information, and the repetition quantity information.