Thermowell may take various forms in engineering applications, such as tapered, straight, and step-shank forms. The thermowells of different shapes have their own characteristics, including their natural vibration frequencies and the stress distributions. The selection of the thermowells shape should be based on the vibration characteristics and the stress distributions. In the past, the designer are eager to learn about the characteristics of different shapes thermowell, but due to lack of analysis of vibration frequency for different shapes thermowell, therefore, in the engineering design, selection of thermowells shape seemed more random. In recent years, with increased discussion and further research on the issue of themowell vibration and stress makes possible to study shapes impact on vibration and stress of thermowell. Based on the ASME PTC19.3 TW-2010, this paper makes analysis and comparison of the natural vibration frequencies and the stress distributions of thermowells of three shapes and provides some guidelines for the selection in engineering applications.