Abstract: The nuclear γ-ray line (GRL) and the proton event (PE) observed in interplanetary space are direct evidences that protons and heavy ions are accelerated to energies above several MeV per nucleon for solar proton flares。 Solar Hard X--ray properties obtained by SMM satellite show there are three classes of solar proton flares: GRL, PE and GRL/PE。 The results indicate the different behavours respect to the hard X--ray properties for the three classes of proton flares seem to be relative with the different height distribution of energetic particles acceleration region (or active region) for the GRL, PE and GRL/PE proton flares。