The load situation of the EMU car bogie frame is complex, and it contains multiple basic load systems under actual operating conditions. Therefore, the damage of the local position of the bogie frame is the accumulation of the corresponding damage of several load systems at that location; the experimental spectrum of the bogie frame is to assess the life of the EMU frame. The bogie frame test spectrum is the key means to assess the life of EMU frame, and how to prepare the test spectrum without measured load is the research goal. In this paper, firstly, the linear assumption, the stability assumption and the typical assumption are researched and confirmed; Then, based on the only dynamic stress data of the long-term measured line, the typical stress of the bogie frame is compiled into a stress spectrum; the load system of the frame is established according to the stress characteristics, and the load stress transfer relationship under each load system is calibrated in the test bench; the maximum calibration coefficient of typical measuring points in the region is taken as the load stress transfer coefficient of the region; then, based on the damage consistency principle, the optimization function is established, and the load stress transfer coefficient matrix obtained is substituted into the optimization function, and a method for deriving the experimental load spectrum from the measured dynamic stress data of transmission lines is established. The test results prove that the method has high accuracy, and the assessment of key parts of the structure has achieved full coverage of typical areas; under the operating conditions of the Chinese line, compared with the international general specifications, this method can achieve damage reproduction in all typical areas. Compiling experimental spectrum is more applicable to the assessment of bogie frame.