Abstract: Starting from dimethyldichlorosilane, tetrahydrofuran and magnesium powder as materials, bis-(4-hydroxybutyl)tetramethyldisiloxane was synthesized. Under different bombardment electron eneries, such as 70 eV, 30 eV and 10 eV, the mass spectra of the title compound is determined with GC/MS. The mass spectrometric analyses indicates that, though molecular ion peak (M +) was not found, but the existence of (M+3) is found. When the bombardment voltage was reduced, the absolute strength of the (M+3) peak declines, and even disappeares.