Addressing the status quo that fault-tolerant logic of composite service is not separated from execution logic and service level agreement (SLA) violation appears frequently, this article proposes a SLA-based fault-tolerant approach for transactional composite services. Firstly, finite-state machine is adopted to model the execution process of the composite service and monitor the execution status. Secondly, monitoring automata is employed to monitor the SLA attributes during its execution to avoid SLA violation. Thirdly, an improved differential evolution algorithm is used to quickly determine the optimal recovery plan for the compensation process. Finally, a process is given to illustrate that as the approach is isolated from the execution logic of the composite service, it is easy to develop, maintain and update. The experimental results based on the real data sets show that the proposed approach is superior to other approaches in both the fault handling time and composition optimization. Meanwhile, the approach can deal with different fault scales.