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Locking mechanism is a popular concurrency control mechanism in distributed computing and database system used to ensure data integrity by prohibiting concurrent conflicting updates on shared data objects. The response of traditional locking is slow, so it can't be used as concurrency controlling strategy for real-time distributed collaborative systems. In this paper, we proposed a responsive fine-grain optimistic locking concurrency controlling algorithm based on relative position for consistency maintenance in real-time distributed collaborative systems. In this algorithm, reading lock and editing lock are taken into account. Moreover, the start position of locking region and the position of operation are relative, and they are not transformed into absolute position until operations are sent to cooperative sites or locks are added into LT. Additionally, the locking granularity can be selected by editors optionally. And any coeditor can edit in advance before his/her requested lock is confirmed. If the request is confirmed, the previous operations go into effect, or else undo these previous operations. In the end, this algorithm is used in our cooperative editing system, and we can find that the possibility of undo the previous editing operations because of locking conflict is very little. So this concurrency controlling algorithm has virtues of quick responsiveness, unconstraint collaboration and nice data consistency maintenance etc.