Abstract: When detecting low-speed target by using mobile sonar platform, the asymmetric reverberation spectrum results in different SRR (Signal Reverberation Ratio) of the positive and negative speed target. Thus, the detection methods have to be separately designed on the two-side reverberation spectrum. However, the asymmetric reverberation spectrum cannot be well described by the traditional symmetric statistical model. Based on two-side exponential symmetric model, the modified asymmetric model is proposed to describe the asymmetric spectrum which might be caused by the motion of platform or moving water surface. The mathematical description of the model is derived, and the physical meaning of each parameter is illustrated. The model is proved by lake experiments to be well fitted to the asymmetric spread spectrum at different speeds of sonar platform. The negative Doppler spread degree is proved aggravated as the platform velocity increases. What's more, the asymmetric model has the capacity of quantitatively describing the Doppler spread degrees of both-side reverberation spectrum.