As an emerging online communication platform, Discord has been widely adopted in the process of open-source software development in recent years. Existing research on Discord proposes specific methods and technologies to help software practitioners efficiently retrieve information, identify duplicate questions in conversation history, and build message datasets to mine valuable information. However, there is still a lack of systematic and comprehensive empirical research on the communication behavior of open-source software practitioners on Discord. The in-depth analysis of this kind of communication behavior is of significance for improving the collaboration efficiency of open-source communities and solving the problems in the process of open-source software development. This study conducts extensive empirical studies on the communication of open-source software practitioners on Discord, constructing two datasets. The first dataset contains 616443 messages from seven open-source software communities, and the second dataset is built on the first dataset via manual selection and validation, containing 17289 high-quality messages. Based on the two datasets, the communication characteristics of open-source software practitioners are systematically characterized from the message and conversation dimensions, including participation, interaction patterns, and discussion topics. Additionally, the influence of these communication characteristics on the response time of conversations and problem-solving status is evaluated. Finally, by combining the research findings, this study summarizes the insights for the design of online communication platforms, proposes recommendations for open-source community management, and points out future research directions for in-depth exploration.