We studied the TOF mass spectra of multiphoton ionhation oftortramethylsilane with ultrasonic molecular beam system at violet laser rebation in thewavelength range of 396～387 urn. In our experimentS, TOF mass spectra showed thatSt (CH3) (n=1, 2, 3), Si+ and C constantly appeated at higher energy laser rebationbut only Si+ and C appeared at lower energy laser radiation. These results indicated thattetramethylsilane had different MPI process under the different laser rebation.