Adiabatic electron affinity (EA) of the CH2Br radical and vibrational frequencies and inversion barrier of the corresponding anion CH2Br-have been calculated using ab initio coupled cluster and hybrid density functional methods with large basis sets up to the augmented correlation-consistent polarized quadruple-zeta (aug-cc-pVQZ) level. The effect of systematic basis set expansion on the calculated EA of CH2Br and inversion barrier of CH2Br- has been investigated with the two theoretical approaches. Electron localization function (ELF) topological analysis of the CH2Br/CH2Br- system is performed to enlighten the process of electron attachment to CH2Br to form CH2Br-.