Abstract: For the necessity of thermal analysis for traveling-wave tube's slow-wave structure, the mechanism of thermal generation in coupled-cavity slow-wave structure has been shown. A professional simulation software combining with the software ANSYS which can do thermal analysis for different type of coupled-cavity slow-wave structure has been designed. Using this software, tube designer can do simulation about thermal performance of coupled-cavity traveling-wave tube's slow-wave structure without the knowledge of how to use ANSYS.