A data packet sending method in an Internet Protocol version 6, IPv6, network, said method being performed by a data packet sending apparatus, said method comprising: determining that a path maximum transmission unit, PMTU, that is of a path that is used by a to-be-sent data packet is unknown; subsequently, sending the to-be-sent data packet on the path according to a minimum maximum transmission unit, MTU; subsequently, probing a path maximum transmission unit, PMTU, of the path; subsequently, sending a subsequent data packet on the path according to the probed PMTU of the path; wherein the performing PMTU probing on the path comprises: constructing a probe packet by using a source IP address and a destination IP address of the to-be-sent data packet, and sending the probe packet on the path; determining whether the sent probe packet is received by a destination receive end of the to-be-sent data packet; and if it is determined that the probe packet is received by the destination receive end, using a maximum MTU used in the probe packet received by the destination receive end as a probed PMTU of the path, characterized in that the minimum MTU is stipulated in the IPv6 protocol, and the probe packet is a transport layer protocol packet, wherein a destination port number of the probe packet is a port number that is not used by the destination receive end, and the performing PMTU probing on the path comprises: after the sending the probe packet on the path, if a peer end unreachable packet is received, determining that the probe packet is received by the destination receive end. determining that a path maximum transmission unit, PMTU, that is of a path that is used by a to-be-sent data packet is unknown; subsequently, sending the to-be-sent data packet on the path according to a minimum maximum transmission unit, MTU; subsequently, probing a path maximum transmission unit, PMTU, of the path; subsequently, sending a subsequent data packet on the path according to the probed PMTU of the path; wherein the performing PMTU probing on the path comprises: constructing a probe packet by using a source IP address and a destination IP address of the to-be-sent data packet, and sending the probe packet on the path; determining whether the sent probe packet is received by a destination receive end of the to-be-sent data packet; and if it is determined that the probe packet is received by the destination receive end, using a maximum MTU used in the probe packet received by the destination receive end as a probed PMTU of the path, characterized in that the minimum MTU is stipulated in the IPv6 protocol, and the probe packet is a transport layer protocol packet, wherein a destination port number of the probe packet is a port number that is not used by the destination receive end, and the performing PMTU probing on the path comprises: after the sending the probe packet on the path, if a peer end unreachable packet is received, determining that the probe packet is received by the destination receive end. constructing a probe packet by using a source IP address and a destination IP address of the to-be-sent data packet, and sending the probe packet on the path; determining whether the sent probe packet is received by a destination receive end of the to-be-sent data packet; and if it is determined that the probe packet is received by the destination receive end, using a maximum MTU used in the probe packet received by the destination receive end as a probed PMTU of the path, characterized in that the minimum MTU is stipulated in the IPv6 protocol, and the probe packet is a transport layer protocol packet, wherein a destination port number of the probe packet is a port number that is not used by the destination receive end, and the performing PMTU probing on the path comprises: after the sending the probe packet on the path, if a peer end unreachable packet is received, determining that the probe packet is received by the destination receive end.