To ensure the relaxed atomicity of transactional composite service (TCS), a lot of relaxed atomicity models have been proposed, but they don’t handle the concurrency control problem specific to their relaxed atomicity model, which can leads to unexpected results when multiple TCS run concurrently. In this paper, we propose a novel concurrency control mechanism to support the user-defined relaxed atomicity model for service composition. Based on the analysis of the two typical kinds of inconsistency caused by cascade compensation and cycle dependency, concurrency control mechanism to confine the forming and changing of dependency is presented, which can eliminate the??inconsistencies while maintaining the relaxed atomicity of individual TCS.