Objective： To develop an internet-based expert diagnostic system for common respiratory diseases. Methods： SaaS system was used to build architecture; pattern of forward reasoning was applied for inference engine design; ASP.NET with C# from the tool pack of Microsoft Visual Studio2005 was used for website-interview medical expert system.The database of the system was constructed with Microsoft SQL Server 2005. Results： The developed expert system contained large data memory and high efficient function of data interview and data analysis for diagnosis of various diseases.The users were able to perform this system to obtain diagnosis for common respiratory diseases via internet. Conclusion： The developed expert system may be used for internet-based diagnosis of various respiratory diseases，particularly in telemedicine setting.