Secret sharing is an effective technique for key management，and has been widely used in many aspects of data security．The existing(k，n)threshold schemes for the secret sharing are relatively complex and the data expansion they cause is remarkable． In this paper，a label assignment method is suggested for reducing the data expansion of a simple threshold scheme．The effect of the improved scheme is obvious and its security is ensured too．Such scheme can be used in the secret sharing of the data on a large scale such as images．