In this paper we extend the concept of the traditional transactor, which focuses on correct content transfer, to a new timing-coherent transactor that also accurately aligns the timing of each transaction boundary so that designers can perform precise concurrent system behavior analysis in mixed-abstraction-level system simulations which are essential to increasingly complex system designs. To streamline the process, we also developed an automatic approach for timing-coherent transactor generation. Our approach is actually applied in mixed-level simulations and the results show that it achieves 100% timing accuracy while the conventional approach produces results of 25% to 44% error rate.