This paper introduces the analysis and test of prestressed flat beams in tube-in-tube concrete structures at different construction stages; moreover, the corresponding structural analysis models with FEA program are set up. Through the comparative analysis between the results of construction field test and that of calculation with FEA method, it proves the reliability of the primary design method; meanwhile, it also indicates that establishment of prestressing force and prestressed effects in similar structures is a complex procedure and should be noticed.