In this peper, the laser power dependence measurement of Si(CH3)4 with parallel plate ionization cell at some wavelengths was reported and the assignment of some transitions in multiphoton ionization(MPI) spectra was discussed. By analysing the pekwidths of time-of-flight (TOF) mass spectra and other experimental results, the possible MPI process of Si(CH3)4 has been studied. It concluded that Si+ mainly came from silicon ionization after neutral molecular fragmentation at higher energy laser radiation, whereas Si(CH3)+n (n=1~3) mainly came from auto-ionization of neutral molecular fragments.