Abstract: A method used of collision induced dissociation (CID) was applied for the studied of fragmentation behavior of three β 2 adrenergic agonists, clenbuterol, salbutamol and SPFF. Electrospray ionization/quadrupole time of flight mass spectrometry (ESI QqTOFMS) in positive ion mode was used to detect three β 2 adrenergic agonist. The standard samples of three drugs were prepared with methanol. The sample with the concentration of 0.1 μg/mL was directly injected into electrospray ionization system. The protonated quasimolecular ion M+H + was selected as internal reference ion for collection. The accurate masses and elemental compositions of the fragment ions were determined. The proposed fragmentation patterns of the mass spectra were explained. The ESI MS 2 analyses indicated that the spectra of the characteristic fragmentations of M+H H 2O +, M+H 74 +, and the common fragment ion of m/z 74 were also found. These characteristics can be used of the future structure elucidation in the studies on metabolism and quantitative analysis of these drugs in human.