The present work is devoted to the study of the excitation of two kinds of Si2O isomers. The results show that the is excitation energies, oscillator strengths, transition electric dipole moments and absorption spectra are affected evidently by external electric field. The triangular Si2O(C2v,1A1) has no visible light absorption spectrum under no external electric field, however, it has faint absorption spectrum(407.18—526.93 nm) in the visible region under external electric field. The linear Si-Si-O(C∞v,3Σ-) has absorption spectra in blue light region and in purple light both in the presence and in the absence of external electric field. One of the important results is that the linear Si-Si-O has strong blue light absorption spectrum(478.88—488.59 nm).