One of the simplest scheme of two-qubit conditional quantum phase gate（CQPG）via a single-mode cavity and a single Λ-type three-level atom have been proposed. The quantum information is encoded on the fock states and of the single-mode cavity and the atomic metastable ground states and of the Λ-type three-level atom. The scheme does not need neither an assistant cavity mode nor an assistant atom to entangle the two qubits of the CQPG，which only requires the resonant coupling between the atomic transition and the cavity mode，so it is much simpler than most of the schemes reported in the past.