A data transmission method, being applied to a terminal device and comprising: performing, in response to arrival of first data at the terminal device during a small data transmission, SDT, procedure, a target interaction with a network device, thereby causing the terminal device to enter a connected state; and transmitting (220, 560), by the terminal device in the connected state, the first data; wherein the SDT procedure is a data transmission procedure of the terminal device in an inactive state, and the first data comprises data not supporting transmission in the SDT procedure, wherein performing the target interaction with the network device, thereby causing the terminal device to enter the connected state, comprises: generating a first data arrival indication by a radio resource control, RRC, layer of the terminal device, wherein the first data arrival indication is used for notifying the network device that the first data arrives at the terminal device; sending the first data arrival indication by performing uplink SDT on an uplink SDT resource, wherein the uplink SDT is uplink data transmission in the SDT procedure; receiving a second message sent by the network device, wherein the second message comprises a connected state indication; and entering the connected state based on the connected state indication, wherein the uplink SDT resource comprises at least one of following resources: a configured grant, CG, uplink resource, and a dynamically scheduled uplink resource. performing, in response to arrival of first data at the terminal device during a small data transmission, SDT, procedure, a target interaction with a network device, thereby causing the terminal device to enter a connected state; and transmitting (220, 560), by the terminal device in the connected state, the first data; wherein the SDT procedure is a data transmission procedure of the terminal device in an inactive state, and the first data comprises data not supporting transmission in the SDT procedure, wherein performing the target interaction with the network device, thereby causing the terminal device to enter the connected state, comprises: generating a first data arrival indication by a radio resource control, RRC, layer of the terminal device, wherein the first data arrival indication is used for notifying the network device that the first data arrives at the terminal device; sending the first data arrival indication by performing uplink SDT on an uplink SDT resource, wherein the uplink SDT is uplink data transmission in the SDT procedure; receiving a second message sent by the network device, wherein the second message comprises a connected state indication; and entering the connected state based on the connected state indication, generating a first data arrival indication by a radio resource control, RRC, layer of the terminal device, wherein the first data arrival indication is used for notifying the network device that the first data arrives at the terminal device; sending the first data arrival indication by performing uplink SDT on an uplink SDT resource, wherein the uplink SDT is uplink data transmission in the SDT procedure; receiving a second message sent by the network device, wherein the second message comprises a connected state indication; and entering the connected state based on the connected state indication, wherein the uplink SDT resource comprises at least one of following resources: a configured grant, CG, uplink resource, and a dynamically scheduled uplink resource.