Abstract: The potential energy surfaces for the cycloaddition reactions of singlet germylene X2Ge(X=H, CH3, F, Cl, Br) and ethylene were studied using density functional theory (DFT). All the stationary points were determined at the B3LYP/6-311G** theory level .The reaction paths from the transition states to both the reactants and products direction were examined by using the intrinsic reaction coordinate (IRC) .A configuration mixing model (CMM) was used to explain the barrier height and the reaction enthalpy .The results showed that the ground state of germylene X2Ge is singlet .The more electronegative the substitutes X in X2Ge are, the larger ΔES-T of X2Ge will be. It is the electronic factors, rather than the steric factors, that play a decisive role in determining the chemical reactivity of germylene .The reactions are in two steps: (1) germylenes and ethylene form an intermediate complex through an exothermal reaction without any barrier; (2) the intermediate complexes isomerize to give the products.