Using atmospheric pressure nitrogen negative corona discharge electron attachment ion mobility spectrometry, the rate constants of electron attachment to CH2 Br2 , CH2 BrCl and CHBr3 were measured at ambient temperature as a function of average electron energy in the range from 0.35 eV to 0.65 eV. The rate constants for electron attachment to CH2 Br2 , CH2 BrCl, CHBr3 follow the relations of k(CH2 Br2 )>k(CH2 BrCl), k(CH2 Br2 )>k(CHBr3 ), and the relations between CH2 Br2 and CH2 BrCl are discussed in theory according to the electron affinity. In addition, the process of electron attachment to CHBr3 is firstly qualitative analyzed. It’s found that when the sample vapor is introduced into the drift region, the bromine ion will cluster with the molecule of CHBr3 to be Br-(H2 O)n (CHBr3 )m.