Multimodal information interfaces contain a variety of audio-visual sensory modal information and dynamic symbolic modal information and are currently the most widely used type of integrated display and control interfaces. However, how to control the complexity of the interface while maximizing the advantages of multimodal fusion of its boundary information has become a design challenge. For both interface designers and users, accurately analyzing and evaluating interface complexity at the design stage is crucial for enhancing usability and effectiveness. Although many methods for analyzing and evaluating visual complexity have been proposed by scholars in recent years, they are not applicable to multimodal information interfaces due to the issues of applicability, practicality and effectiveness. To address this gap, after reviewing and analyzing these related studies on interface complexity, we deeply analyze the focus and dimensions of evaluating the complexity of multimodal information interfaces based on analytical methods. Building upon existing factors and experts’ evaluations, we propose a more comprehensive and structured classification of complexity factors, along with complexity evaluation metrics and evaluation process for multimodal information interfaces. The proposed complexity evaluation method is widely applicable, employing a series of measures is both universal and user-friendly. This framework serves as a valuable reference for optimizing multimodal information interfaces, ensuring a balance between information integration and usability.