A data transmission method, wherein the method comprises: obtaining, by a first terminal device, first data from a base station based on a first identifier, wherein the first identifier is used to identify a first cooperation group, and the first cooperation group comprises the first terminal device and a second terminal device; and forwarding, by the first terminal device, the first data to the second terminal device, wherein the method further comprises: receiving, by the first terminal device, the first identifier from the base station, wherein the obtaining, by a first terminal device, first data from a base station based on a first identifier comprises: receiving, by the first terminal device, a data packet from the base station, and descrambling, by the first terminal device, the data packet based on a scrambling code sequence that is determined by using the first identifier, to obtain the first data, wherein an initial sequence corresponding to the scrambling code sequence is a 31-bit binary sequence, 16 most significant bits of the initial sequence are a binary sequence of the first identifier, a 17 th bit of the initial sequence is a binary sequence of a transport block quantity identifier, and 10 least significant bits of the initial sequence are a binary sequence of a data scrambling identifier, wherein the transport block quantity identifier is used to indicate a quantity of transport blocks comprised in the first data, and the data scrambling identifier is configured by the base station, or the data scrambling identifier is a physical layer cell identifier. obtaining, by a first terminal device, first data from a base station based on a first identifier, wherein the first identifier is used to identify a first cooperation group, and the first cooperation group comprises the first terminal device and a second terminal device; and forwarding, by the first terminal device, the first data to the second terminal device, wherein the method further comprises: receiving, by the first terminal device, the first identifier from the base station, wherein the obtaining, by a first terminal device, first data from a base station based on a first identifier comprises: receiving, by the first terminal device, a data packet from the base station, and descrambling, by the first terminal device, the data packet based on a scrambling code sequence that is determined by using the first identifier, to obtain the first data, wherein an initial sequence corresponding to the scrambling code sequence is a 31-bit binary sequence, 16 most significant bits of the initial sequence are a binary sequence of the first identifier, a 17 th bit of the initial sequence is a binary sequence of a transport block quantity identifier, and 10 least significant bits of the initial sequence are a binary sequence of a data scrambling identifier, wherein the transport block quantity identifier is used to indicate a quantity of transport blocks comprised in the first data, and the data scrambling identifier is configured by the base station, or the data scrambling identifier is a physical layer cell identifier. receiving, by the first terminal device, the first identifier from the base station, wherein the obtaining, by a first terminal device, first data from a base station based on a first identifier comprises: receiving, by the first terminal device, a data packet from the base station, and descrambling, by the first terminal device, the data packet based on a scrambling code sequence that is determined by using the first identifier, to obtain the first data, wherein an initial sequence corresponding to the scrambling code sequence is a 31-bit binary sequence, 16 most significant bits of the initial sequence are a binary sequence of the first identifier, a 17 th bit of the initial sequence is a binary sequence of a transport block quantity identifier, and 10 least significant bits of the initial sequence are a binary sequence of a data scrambling identifier, wherein the transport block quantity identifier is used to indicate a quantity of transport blocks comprised in the first data, and the data scrambling identifier is configured by the base station, or the data scrambling identifier is a physical layer cell identifier. receiving, by the first terminal device, a data packet from the base station, and descrambling, by the first terminal device, the data packet based on a scrambling code sequence that is determined by using the first identifier, to obtain the first data, wherein an initial sequence corresponding to the scrambling code sequence is a 31-bit binary sequence, 16 most significant bits of the initial sequence are a binary sequence of the first identifier, a 17 th bit of the initial sequence is a binary sequence of a transport block quantity identifier, and 10 least significant bits of the initial sequence are a binary sequence of a data scrambling identifier, wherein the transport block quantity identifier is used to indicate a quantity of transport blocks comprised in the first data, and the data scrambling identifier is configured by the base station, or the data scrambling identifier is a physical layer cell identifier.