A first terminal device, comprising: a sending unit, configured to send a first Media Access Control, MAC, protocol data unit, PDU, by using a first resource block, wherein the first MAC PDU carries a first reservation indicator field, so as to instruct the first terminal device to reserve the first resource block; a receiving unit, configured to receive a second MAC PDU sent by using a second resource block by a set of second terminal devices, wherein the set of second terminal devices comprises at least one second terminal device, and the second MAC PDU carries a first resource feedback field, so as to indicate that the first resource block is successfully reserved; and a determining unit, configured to determine, according to the first resource feedback field that is received by the receiving unit and that is sent by the second terminal device in the set of second terminal devices, that the first resource block used by the sending unit to send the first MAC PDU is a resource block used to send a new MAC PDU; wherein the sending unit is further configured to send the new MAC PDU by using the first resource block determined by the determining unit; wherein, the first terminal device further comprises: a monitoring unit, configured to monitor a contention resource pool before the sending unit sends the first Media Access Control MAC protocol data unit PDU by using the first resource block; wherein the determining unit is further configured to determine a second resource feedback field according to a reservation status that is of a resource block in the contention resource pool and that is obtained by the monitoring unit by means of monitoring, wherein the second resource feedback field is used to indicate the reservation status of the resource block in the contention resource pool before the first MAC PDU is sent; and the first MAC PDU sent by the sending unit by using the first resource block further carries the second resource feedback field. a sending unit, configured to send a first Media Access Control, MAC, protocol data unit, PDU, by using a first resource block, wherein the first MAC PDU carries a first reservation indicator field, so as to instruct the first terminal device to reserve the first resource block; a receiving unit, configured to receive a second MAC PDU sent by using a second resource block by a set of second terminal devices, wherein the set of second terminal devices comprises at least one second terminal device, and the second MAC PDU carries a first resource feedback field, so as to indicate that the first resource block is successfully reserved; and a determining unit, configured to determine, according to the first resource feedback field that is received by the receiving unit and that is sent by the second terminal device in the set of second terminal devices, that the first resource block used by the sending unit to send the first MAC PDU is a resource block used to send a new MAC PDU; wherein the sending unit is further configured to send the new MAC PDU by using the first resource block determined by the determining unit; wherein, the first terminal device further comprises: a monitoring unit, configured to monitor a contention resource pool before the sending unit sends the first Media Access Control MAC protocol data unit PDU by using the first resource block; wherein the determining unit is further configured to determine a second resource feedback field according to a reservation status that is of a resource block in the contention resource pool and that is obtained by the monitoring unit by means of monitoring, wherein the second resource feedback field is used to indicate the reservation status of the resource block in the contention resource pool before the first MAC PDU is sent; and the first MAC PDU sent by the sending unit by using the first resource block further carries the second resource feedback field. a monitoring unit, configured to monitor a contention resource pool before the sending unit sends the first Media Access Control MAC protocol data unit PDU by using the first resource block; wherein the determining unit is further configured to determine a second resource feedback field according to a reservation status that is of a resource block in the contention resource pool and that is obtained by the monitoring unit by means of monitoring, wherein the second resource feedback field is used to indicate the reservation status of the resource block in the contention resource pool before the first MAC PDU is sent; and the first MAC PDU sent by the sending unit by using the first resource block further carries the second resource feedback field.