The invention is directed to a wireless sensor network system. The wireless sensor network system is adapted for a medication information security environment, and the wireless sensor network system comprising a first sensor node, a second sensor node and a central node. The first sensor node sends a request for registration and a user identification. The central node generates and stores a first set of random number and a second set of random number when receiving the request for registration and the user identification. The central node sends the first set of random number and the second set of random number to the first sensor node and the second sensor node respectively.