A system for combining wireless sensor networks includes a first sink transmitting a request to combine (RTC) and first routing-information. First nodes propagate data and instructions in a first wireless sensor network. The first nodes broadcast the RTC when the first nodes are boundary nodes. The first routing-information are established based on first transmission paths between the first sink and the first nodes. A second sink receives the RTC and the first routing-information from the first sink. The second sink transmits second routing-information to the first sink. The second routing-information are established based on second transmission paths between the second sink and the second nodes. The second node relays the RTC to the second sink according to a flag in a packet of the RTC. The first wireless sensor network combines with the second wireless sensor network to exchange the first routing-information and the second routing-information.