Density functional (B3LYP) calculations using the 6-31++g** basis set have been employed to study the title reaction between the cationic 1,3-dipolar 1-aza-2-azoniaallene ion (H2CdN+dNH) and ethene. Our calculations confirmed that [3 + 2] cycloaddition reaction takes place via a threemembered ring intermediate. In addition, solvent effects and substituent effects were also studied. For the reactions involving tetrachloroethene, there are two attacking sites. One is on the NH group in the 1-aza-2-azoniaallene ion, another is on its terminal CH2 group, and they are competitive for both approaching positions. Electron-releasing methyl substituents on ethene favor the reaction, and the potential energy surface is quite different from the previous one.