[en] Nuclear codes have detailed regulations on the mechanical analysis of nuclear Class 1 piping. But limited calculation facilities restrict the analysis of Class 1 piping, so that design safety requirements are not satisfied. This paper discusses the mechanical analysis of Class 1 piping using general-purpose finite element software. The general-purpose finite element software MARC is used to analyze a Class 1 piping system in HTR-10 to introduce the procedure for mechanical analysis and safety evaluation. The objective is to satisfy the regulations for the Class 1 piping in nuclear codes. The method introduced in this paper can be used as a practical method for mechanical analysis of a nuclear Class 1 piping