A method for packet transmission in an MIP network is disclosed. A mobile node sends to a Home Agent (HA) a first Firewall Detection (FD) packet encapsulated with IP security (IPsec) protocol and a second FD packet encapsulated with the IPsec protocol and User Datagram Payload (UDP) protocol. The mobile node determines whether there is a firewall blocking an IPsec packet between the mobile node and the HA according to a Firewall Detection Reply (FDR) packet from the HA. If there is a firewall, packets are encapsulated with the UDP protocol and binding update and packet exchange are performed; otherwise, binding update and packet exchange are performed. A mobile node for packet transmission is also provided. Embodiments of the present invention enables the mobile node to exchange a packet with a correspondent node when there is a firewall not supporting the IPsec protocol between the mobile node and the HA.