Abstract: In this paper,following the analysis of some concurrency control algorithms frequently used in DDBMS,we point out that Primary Copy Locking (PCL) concurrency control algorithm is si- mple,efficient,and easy to implement in the environment of microcomputers and local network An improved PCL algorithm is proposed to overcome the deficiencies of ordinary PCL The data structure. locking algorithm,deadlock detection and copy updating of the improved PCL algorithm are discussed.