The velocity distribution of emission electrons in the transfer ionization process of 70keV He2+ colliding on He has been studied with a reaction microscope. These distributions show that the electrons lie mainly in the scattering plane which are observed to be emitted preferentially in the forward direction, lying between 0 and projectile velocity Vp. The distributions also display a typical two-fingered structure with a local minimum on internuclear axis. This characteristic can be qualitatively explained as being due to the interference between σ amplitude and π amplitude of electrons final wavefunction. It depends also on the impact parameters; the π amplitude contribution is dominant at small impact parameters, which leads to a symmetric velocity distribution around the internuclear axis. However, at large impact parameters the σ amplitude contribution increases relatively obviously, resulting in an asymmetric electrons velocity distribution around the internuclear axis.