A data transmission method, applied to a terminal comprising a PDCP layer entity, a first RLC layer entity, a second RCL layer entity and a MAC layer entity, wherein the method comprises: when detecting that a data duplication transmission function of the PDCP layer entity is activated, enabling (2a01,2b03) the first RLC layer entity, wherein the second RLC layer entity is in an enabled status; and invoking the PDCP layer entity to determine a first PDCP PDU associated with a first PDCP SDU, and sending the first PDCP PDU to the first RLC layer entity (2a02), wherein the first PDCP PDU is configured for the first RLC layer entity and the MAC layer entity to process the first PDCP PDU into a MAC PDU and send the MAC PDU (2a03,2b05), wherein after enabling (2a01) the first RLC layer entity when detecting that the data duplication transmission function of the PDCP layer entity is activated, the method further comprises: when detecting that the PDCP layer entity receives a second PDCP SDU, invoking (2c01) the PDCP layer entity to encapsulate the second PDCP SDU into a second PDCP PDU; and invoking (2c02) the PDCP layer entity to send the second PDCP PDU to the first RLC layer entity and the second RLC layer entity, and wherein after sending the second PDCP PDU to the first RLC layer entity and the second RLC layer entity, the method further comprises: when detecting that the data duplication transmission function of the PDCP layer entity is deactivated, invoking (2c03) the PDCP layer entity to send a preset indication to the first RLC layer entity; and characterised by invoking the first RLC layer entity (2c04) to receive the preset indication, and discarding a second RLC SDU in the first RLC layer entity and corresponding to the second PDCP PDU according to the preset indication, in case that the second RLC SDU is not encapsulated and processed into a second RLC PDU by the first RLC layer entity. when detecting that a data duplication transmission function of the PDCP layer entity is activated, enabling (2a01,2b03) the first RLC layer entity, wherein the second RLC layer entity is in an enabled status; and invoking the PDCP layer entity to determine a first PDCP PDU associated with a first PDCP SDU, and sending the first PDCP PDU to the first RLC layer entity (2a02), wherein the first PDCP PDU is configured for the first RLC layer entity and the MAC layer entity to process the first PDCP PDU into a MAC PDU and send the MAC PDU (2a03,2b05), wherein after enabling (2a01) the first RLC layer entity when detecting that the data duplication transmission function of the PDCP layer entity is activated, the method further comprises: when detecting that the PDCP layer entity receives a second PDCP SDU, invoking (2c01) the PDCP layer entity to encapsulate the second PDCP SDU into a second PDCP PDU; and invoking (2c02) the PDCP layer entity to send the second PDCP PDU to the first RLC layer entity and the second RLC layer entity, and wherein after sending the second PDCP PDU to the first RLC layer entity and the second RLC layer entity, the method further comprises: when detecting that the data duplication transmission function of the PDCP layer entity is deactivated, invoking (2c03) the PDCP layer entity to send a preset indication to the first RLC layer entity; and characterised by invoking the first RLC layer entity (2c04) to receive the preset indication, and discarding a second RLC SDU in the first RLC layer entity and corresponding to the second PDCP PDU according to the preset indication, in case that the second RLC SDU is not encapsulated and processed into a second RLC PDU by the first RLC layer entity. when detecting that the data duplication transmission function of the PDCP layer entity is deactivated, invoking (2c03) the PDCP layer entity to send a preset indication to the first RLC layer entity; and characterised by invoking the first RLC layer entity (2c04) to receive the preset indication, and discarding a second RLC SDU in the first RLC layer entity and corresponding to the second PDCP PDU according to the preset indication, in case that the second RLC SDU is not encapsulated and processed into a second RLC PDU by the first RLC layer entity.