声光器件衍射光峰值偏转位置与输入信号频率成正比是声光频谱仪测频的基本原理，但实际中衍射的非线形效应会引起衍射光峰值偏转误差较大。为减小频率测量方差，需对衍射光强数据做相应处理。对CCD背景噪声的数字特征分析，以背景噪声数学平均值为阈值做去噪处理。根据最小二乘法原理，对衍射光强数据做一次高斯函数拟合，拟合数据与光强数据相关系数为0.997 6。在现有测试光学平台下，根据衍射光强峰值位置估计的频率测量方差为542.5 kHz2，利用拟合高斯函数中心值估计的频率测量方差为31.8 kHz2。为减小声光频谱仪频率测量方差提供了理论支持。

Diffraction beam deflection peak position of the acousto-optic device is proportional to the input signal frequency. It is the basic theory for acousto-optic spectrum analyzer frequency measurement. But the non-linear effects in diffraction causes diffraction peak deflection error. To get better measurement results, the diffraction intensity data should be processed to reduce the frequency of measurement variance. After the digital features of CCD background noise were analyzed, the background noise mathematical average had been taken as the threshold when denoising the data of diffraction intensity. According to the principle of least square method, fitting the diffraction intensity data by Gaussian function, the correlation coefficient is 0.997 6. Under the existing optical experimental platform, the measure variance is 542.5 kHz2 while the frequency was estimated by the diffraction peak position; the measure variance is 31.8 kHz2 while the frequency was estimated by the middle value of Gaussian fitting function. It provides theoretical support for reducing the frequency measurement variance of acousto-optic spectrum analyzer.