Abstract: The optical spectra from the interaction between a 30 fs, 1×1019 W/cm2 laser pulse and foil targets on SILEX-Ⅰ are studied. Evident red shifts of the second and three-half harmonic emissions in the specular reflection direction are observed from a 3 μm thick copper target. The recession velocity at the reflection surface is deduced to be 2.6×108 cm/s. For the 200 nm thick CH target, a supercontinuum extending from 300 to 940 nm is observed in the direction of laser propagation. The density distribution of plasmas induced by laser prepulse is simulated using MULTI-1D hydrodynamic code. The results show that, laser prepulse has a profound effect on the pre-plasma density distribution of a foil target, which leads to the differences in the observed spectra.