The study shows that, the vibration of structures and members has very obvious self-excited vibration characteristic under the action of fire. Random signals for acceleration distribution of composite beams of the overall structure under the action of fire are collected and auto-spectrum analyzed in this paper. The result shows that: the fire causes self-excited vibration of composite beams of the overall structure. As the internal forces cause re-distribution and structure connections are damaged, amplitude, frequency and vibration characteristic excited by external forces of composite beams are different, and fluctuating decrease occurs to vibration frequency of composite beam in the test. Test results provide data support for the establishment of fire vibration theory and healthy detection of structures in case of fire.