There are unknown impurities and defects usually in unintentionally undoped GaN film due to imperfect growth procedures so that the luminescence related to the energy levels of the unknown impurities and defects occurs. The red luminescence of undoped GaN film at 692 nm is reported. The emitting mechanisms of blue and red luminescence of undoped GaN film are studied. The energy levels of initial states of blue and red luminescence are measured directly in experiments by using a novel absorption-normalized photoluminescent excitation spectroscopy proposed by the authors. It is determined that the blue luminescence originates from the transition of donor to valence band, and the red luminescence is caused by the recombination of donor to acceptor. A complete luminescent model is built up for the blue, yellow and red luminescence of undoped GaN film. The gotten results have important reference values for determination of types of the unknown impurities and defects.