In allusion to the frequency modulation to amplitude modulation (FM-to-AM) effect in the transmission process of small broadband frequency modulation pulse, variation of pulse waveform and characteristics caused by loss of different orders in the spectrum is studied, combining theoretical simulation with experimental validation. The results show that the waveform modulation increases linearly with the loss of spectral component, and the outline of waveform modulation is associated with the positions of the missing spectral components in the spectrum. The results provide the basis of precompensation and inhibition of FM-to-AM effect, and make a certain significance for safe operation of laser facility and improvement of physical experiment results.