By the counterpoise-correlated potential energy surface method (interaction energy optimization), five structures of the C2H4-nFn-HF (n=0,1,2) dimers with all real frequencies have been obtained at MP2/aug-cc-pVDZ level. The influence of F substituent effect on the structure and pi-hydrogen bond of dimer has been discussed. For C2H4-nFn-HF (n=1,2), the pi-hydrogen bonds are elongated comparing with that for C2H4-HF. For C2H3F-HF, g-C2H2F2-HF, cis-C2H2F2-HF, the pi-hydrogen bonds are further deformed. These changes (elongate, shift, and deformation) of pi-hydrogen bond mainly come from deformation of pi-electron cloud of C=C bond. The pi-electron cloud is pushed towards the one C atom, the pi H-bond shift also to the C direction. Since the two lobes of pi-electron cloud have deviated slightly from the molecular vertical plane passing through C=C bond, the pi-hydrogen bond is sloped. Intermolecular interaction energies of the dimers are calculated to be -3.9 for C2H4-HF, -2.8 for C2H3F-HF, -2.1 for g-C2H2F2-HF, -1.6 for cis-C2H2F2-HF, -1.3 kcal/mol for trans-C2H2F2-HF, at CCSD(T)/aug-cc-pVDZ level. (C) 2004 American Institute of Physics.