Combing the theory of acoustooptic modulation and STFT, the spectrum measurement of high bandwidth signal can be realized by acoustooptical spectrum analyzer. In this algorithm, the transient frequency domain parameters of the signal can be acquired by using the spatial Fourier transform data of the detected signal in the transient spacetime correlation output and processing. The simulation results show that the frequency reduction rate is greater than 99.5%; the signal detection rate is less than 0.2%.