Wireless Sensor Network (WSN) is the well growing technology in the fields of defence, industrial automation, building automation, environmental forecasting, asset management, health care etc. In WSN, each and every node should be secured and this security is achieved by secure group communication. There are many key management techniques used to implement group communication in a secured manner but the key distribution is always being an issue in WSN because of limited capabilities and vulnerable nature of WSN. The proposed WSN totally uses three sort of keys namely Master key, session key and pair wise keys for secured communication are used in WSN. The main goal is to provide secured node to node communication by using efficient pair wise keying mechanism and it uses secret code for secure communication. It provides the better robustness, authentication and more security. The proposed WSN architecture has two hierarchy layers known as H end and L end sensor layers in a cluster. Secured communication between Low end node (L) to Low end node (L) and High end node (H) to High end node (H) follows efficient pair wise keying mechanism. To establish secured communication between Low end node (L) to High end node (H) and Cluster Head (CH) to Cluster Head (CH), new node key should be established before establishing pair wise keying mechanism. Master key is established for the broadcasting of Base Station (BS) to all other nodes. In performance analysis, computation, communication and storage cost are calculated and analysed.