We report a theoretical study of electronic transport properties of α-T3 lattice nanoribbons in the presence of uniform electric and magnetic fields. Landau levels with an unexcepted fashion are obtained in the system, and unique flat bands are observed due to the crossed electric and magnetic fields. We found that the nondispersive flat band of α-T3 lattice is distorted and split to many dispersive energy levels when electric and magnetic fields are applied. A double constriction structure of α-T3 lattice is considered to investigate the quantum transport in the flat band, and novel quantum transport properties are obtained, which shows great differences from conventional Dirac electrons. Our results show that the flat bands of α-T3 lattice can also contribute to the quantum transport properties and play an important role in the development of novel Dirac electron device.