The embodiment of the invention discloses an external communication method, device and system for a 6LoWPAN (internet protocol 6 over low power wireless personal area network) intra-network device and the outside. The method comprises: receiving a data packet sent by the intra-network device, wherein the header of the data packet carries a source address, a destination address and an external forwarding mark, the source address of a link layer header and the source address of an adaptation layer header are addresses of the intra-network device, and the destination address of the link layer header and the destination address of the adaptation layer header are addresses of a gateway device; acquiring the home address of the corresponding external network device; rewriting the destination address of the adaptation layer header of the data packet as the home address of the external network device, and packaging again; and transmitting the data packet after being packaged again to the external network device. The invention is suitable for compressing the header for the data packet when the intra-network device and external network device of the 6LoWPAN network communicate with each other.