A detailed theoretical study of the potential energy surface of poorly understood ion-molecule reaction of NH2- and O-2 (a(1)Delta(g)) is explored at the density functional theory B3LYP/6-311++G(d,p), ab initio of QCISD/6-311++G(d,p) and CCSD(T)/6-311++G(3df, 2pd) (single-point) theoretical levels for the first time. It is shown that there are six total possible products from P-1 to P-6 on the singlet potential energy surface. Among these, the charge-transfer product P-1 (NH2 + O-2(-)) is the most favorable product with predominant abundances, whereas P-4 (NO- + H2O) and P-2 (HNO + OH-) may be the second and third feasible products followed by the almost neglectable P-3 (NO2- + H-2), while P-s (c-NO2- + H-2) and P-6 (ONO- + H-2) will not be observed due to their either high barriers or being secondary products. The present theoretical study points out that besides P-1 (NH2 + O-2(-)) and P-2 (HNO + OH-), P-4 (NO- + H2O) should be also observed, which is different from the previous experiment study by Anthony Midey et al. in 2008. In addition, almost all of the reaction pathways to products are exothermic and the reaction rate should be very fast since the reaction barriers are very low except for P-s (c-NO2- + H-2) which is in agreement with the measured total reaction rate constant k = 9.0 x 10(-10) cm(3)s(-1) at 300 K in the experiment study. It is expected that the present theoretical study may be helpful for the understanding of the reaction mechanism related to NHX-, NX2-, PHX-, and PX2- (X = H, F, and Cl).