The present paper describes transient thermal and mechanical analyses of a lox/kerosene type turbopump in a LRE(Liquid Rocket Engine). Turbopumps are used to pressurize propellants to achieve higher specific impulse of LRE. The turbopump under development has been designed and verified by structural analyses using finite element methods. Some parts of the turbopump operate under cryogenic environments, while the others work under ambient and high temperature environments. Therefore, numerical analysis at a turbopump system level is essential. In this study, casing assemblies of lox pump and fuel pump were analyzed to determine strength test and air-tightness test conditions. Also, some operational stress and strains of fuel pump casings were measured and analyzed. Based on these results, stress concentration of fuel pump casings during the operation could be successfully predicted.