Abstract: Deterministic network technology like Time-triggered Ethernet (TTE) and Time-sensitive Networking (TSN) is gradually applied to mission critical systems such as avionics, industrial automation and vehicle mounted systems. Time synchronization technology is the essential precondition for these networks’ proper functioning. Nevertheless, there is no analytical model nor comparative analysis for the reliability of time synchronization services in different protocols. Aiming at this problem, we analyze the time synchronization process of the two protocols of above-mentioned networks, and extract the factors that lead to the failure. Then, we propose a theoretical evaluation model of the failure probability for these two protocols. On this basis, the failure scenario and failure probability are compared and analyzed. Finally, we use OPNET simulator to verify the consistency with the theoretical analysis. The time synchronization failure probability evaluation model proposed in this paper can provide reference for relevant personnel.