Objective To investigate the characteristics of acoustic parameters and spectrograph of varying laryngeal diseases and discuss the value of acoustic analysis technique by computer in the quantitative and objective evaluation of vocal function.Methods The voice signals of sustained vowel "a" were measured with a computer (Dr.Speech software) in 78 healthy adults and 98 patients with varying laryngeal diseases.The acousic parameters (jitter,shimmer and NNE) and spectrographic characteristics (harmonic waves,formants and noise) were analyzed.The resubs obtained by acoustic technique were compared with those of perceptual evaluation.Results The acoustic parameters were significantly increased in all patients with laryngeal diseases.The mean parameters were increased 0.5～1.5 times in vocal inflammation and 2.0～4.5 times in vocal paralysis or laryngeal carcinoma as much as the control group.The spectrogarph in laryngeal diseases showed irregularity,breakage or lack of harmonic waves and formants,and increase of noise.A three-point scale was used to rate the pathologic spectrograph and coincided with the degrees of hoarseness judged by perceptual analysis.Conclusion The acoustic parameters and spectrograph can be used as objective standards for evaluaing voice function quantitatively.The acoustic analysis by computer technique is of value in the diagnosis and treatment of laryngeal diseases.