Increasing importance of FlexRay systems in automotive domain inspires unceasing comparative researches. One primary issue among researches is to verify the reliability of FlexRay systems either from protocol aspect or from system design aspect. However, for more precisely addressing the FlexRay system reliability issue, we require a more generic analysis that simultaneously considers the network topology, clock sync between FlexRay ECUs and the ECU fault-tolerance. To fulfill this requirement, in this paper we first apply a well-known reliability model, Dynamic Fault Tree (DFT), to model the reliability of FlexRay systems with various network topologies, and then employ the Markov Chain (MC) to model the reliability of clock sync in terms of the number of sync ECUs. Furthermore, various fault-tolerant techniques for ECUs protection are also modeled by MC. The adopted two reliability models, DFT and MC, are integrated to form a mixed DFT to assess the FlexRay system reliability more accurately. Through a FlexRay steer-by-wire case study, we demonstrate the influence of different topologies, different ECU fault-tolerance and various number of sync ECUs on the reliability of FlexRay steer-by-wire system.