An unknown compound in petroleum aromatics was analyzed by Fourier transform ion cyclotron resonance mass spectrometry(FT-ICR MS) coupled with atmospheric pressure photoionization(APPI)，electrospray ionization(ESI) and direct analysis in real time(DART) ionization.It was determined as tris(2，4-di-tert-butylphenyl)phosphate(TDTBPP) by the accurate mass of FT-ICR MS and collision activated dissociation(CAD).The characteristic spectra of TDTBPP in multiple ionization sources were demonstrated.The result indicated that the main mass peak in APPI was ［M+H］+，and M.+ was also present.The main mass peak in ESI was ［M+Na］+(without formic acid) or ［M+NH4］+(with formic acid)，and the main mass peak in DART was ［M+NH4］+.APPI FT-ICR MS could be used to determine the polycyclic aromatic hydrocarbons(PAHs) with relatively higher molecular weight which could not be determined by gas chromatography-mass spectrometry.