With the effective Thomson scattering diagnostic of the laser plasmas produced under different laser conditions, the distinct asymmetry of the two peaks of the ion-acoustic waves are measured 150 μm in front of the target surface. The more intense peak appears at shorter wavelength when the electron temperature is higher, and switches to longer wavelength when the electron temperature is lower. The two-peak strcture, the asymmetry and the position of the more intensity peak of the ion-acoustic waves can be well interpreted with the Raman scattering effect. This paper, for the first time, establishes the corresponding relationship between Raman scattering of light and Thomson scattering of electons in laser plasmas.