Time-integrated spectra of second harmonic (2w ) light emission from plasmas produced with 1.053m m laser are simultaneously measured at several scattering-angles on Xingguang II laser facility. The spectra show that 2w light is just due to resonance absorption, and ion-acoustic decay instability is suppressed. The mean velocity of critical surface and its variation during laser pulse are inferred from the spectra. Moreover, the relationship between scattered light intensity and scattering angle is also acquired.