Abstract: In the LCA (level-crossing algorithm), deleting a large number of channel characteristic sequences causes a waste of resources, and at the same time the key generation rate is low. Therefore, a new improved method based on LCA is proposed. The algorithm’s performance was improved by preprocessing. An m-length window was added to the obtained position index set, and matching search and threshold judgment were performed on the sequence range retained after windowing. The maximum and minimum values were parsed to obtain circular decision to generate key bits. The simulation experiment results show that the key inconsistency rate of the improved algorithm is even slightly better than that of the LCA algorithm at high signal-to-noise ratio, and the key generation efficiency KGE is increased by about 4 times, which has a significant advantage in key length.