Abstract: The float rotameter FT011 is a new type of flow measuring equipment applied in nuclear power plant AP1000 by horizontal installation. Because the extending direction of the pipe is uncertain, so is the installation direction of the rotameter, there are many directions along which the seism and nozzle loads are applied to the rotameter. Many installation locations should be considered for the stress analysis, and the worst combination of the loads should be gained so that the results can envelop all the working condition. The analysis is more complicated because of the eccentric loads of the indication meter. According to the structural characters, the rules applying the constant loads firstly and then the variable loads were obeyed in this paper, and the methods of applying the variable loads were complied with the starting points that the stress effects should be the same as each other. The worst combination of the loads applied to the tube and the bolts were gotten at last. The combination methods of uncertain loads can be referenced by the concerned stress analysis of the nuclear engineering.