Key management in Wireless Sensor Network (WSN) is a complex task due to its nature of environment, limited resources and open communication channel. In addition, wireless communication poses additional threats to the critical information being sent and received over there. WSN are necessary to be protected from different attacks. But, the major problem to secure WSN is a key distribution after deploying the sensor nodes in specific area. This paper examines the design of an efficient key management distribution scheme for WSN. The proposed method based on knapsack algorithm that requires generating a series of vectors to encrypt the private keys only that will be sent to the cluster heads by base station. The same method is used by each cluster head to encrypt only the keys that will be sent to their members. The simulation results showed that the proposed key management method can offers efficient security prerequisites, suitable scalability, and connectivity to achieve authentication..