Disclosed are a key managing system and method for sensor network security. The key managing system includes a secret key transmitter configured to transmit a portion of a secret key map, stored in a node, to a correspondent node, and transmit the secret key map of the node to the correspondent node by using the transmitted portion of the secret key map and an authenticator configured to acquire a trust level of the correspondent node which indicates a ratio of a total size of the secret key map of the node and a size of the secret key map transmitted to the correspondent node, compare the acquired trust level of the correspondent node and a threshold value, and authenticate the correspondent node and a message acquired from the correspondent node by using the comparison result.