Abstract: Usability evaluation model was constructed for in-car instant messaging applications with multimodal interactions, and optimization suggestions were proposed based on evaluation results. With research in human-machine interface and usability, usability principles including “clear and easy to operate”, “efficient and practical”, and “safe” were determined, and 15 indexes were defined accordingly. Usability evaluation tests were conducted on three cars by building a real-vehicle driving simulation platform innovatively. Combining AHP and CRITIC method, index weights were determined dynamically by considering subjective opinions and objective data performance, and evaluation model was built by applying fuzzy comprehensive evaluation. Finally, problems such as visual and manual distraction caused by touch-screen interaction negatively affecting safety, and task completion time of voice interaction directly affecting user trust and thus driving performance, etc. were identified, and targeted design suggestions were put forward. The real-vehicle driving simulation platform and evaluation model can be used to test the usability of and evaluate more interaction models, tasks and infotainment applications, and thus guide experience design.