Abstract: The Controller Area Network (CAN)-Time Sensitive Networking (TSN) gateway serves as a crucial element in the end-to-end transmission path for transmitting critical service data in the next-generation in-vehicle network architecture. Its real-time performance has a direct impact on the ability to schedule messages transmitted across heterogeneous network systems. However, existing studies on the real-time performance of CAN-TSN gateways face urgent issues, such as incomplete consideration of gateway processing delays and a lack of joint analysis of scheduling planning results for TSN networks. As a result, the schedulable set obtained using existing studies often fails to meet end-to-end deadline constraints. To address these issues, a real-time analysis method for CAN-TSN gateways based on joint planning is proposed. The method constructs a general architecture based on the existing CAN-TSN gateway architecture design and analyzes the composition of gateway processing delays to obtain a parametric model of processing delay. The proposed method derives an upper bound on the gateway delay that satisfies the end-to-end schedulability of messages by combining the planning and scheduling results of TSN networks. Furthermore, the proposed method builds a CAN-TSN gateway prototype system and uses a real TSN gateway prototype system to perform schedulability analysis using real in-vehicle CAN message sets. The experimental results show that the proposed method can tighten the schedulable range of CAN message sets in a real environment, resulting in a schedulable rate tightening of approximately 6.7%. The proposed method can also guide the optimization of the gateway's real-time architecture.