Combing the techniques of supersonic molecular beam and vacuum ultraviolet synchrotron radiation photoionization time-of-flight mass spectroscopy,we have measured the photoionization efficiency(PIE)curves of ions from (CH3I)n(n=1,2,3,4)cluster molecules and obtained the adiabatic ionization potentials of (CH3I)n+(n =1,2,3,4) and appearance potentials of the fragment ions.From these data,bond energies D0 of the related molecules or molecule ions have been evaluated.Several autoionization structures of CH3I in the PIE curve of CH3I+ have been observed and 4 Rydberg series,ns,npσ, npπ and nd, converging to CH3I+(2Ｅ1/2),are identified.