RHEED is one of the powerful tools for surface studies and monitoring thin film growth. RHEED pattern provides information on surface structures, surface morphology and thin film crystallography. Further more information including inelastic scattering can be obtained by installation of energy-filter in RHEED apparatus. We present a newly constructed energy-loss measurement system for diffracted electrons and demonstrate the experimental data obtained from Si(111)7×7 surface. For the morphology of regular step surface, it is shown that the mean terrace length can be evaluated by the energy-filtered RHEED pattern of the vicinal Si surface. Reflected electron beams from a specimen surface into vacuum are usually concerned in conventional RHEED. On the other hand, it is shown that the incident electron density distribution (wave field) formed in a crystal surface is useful to clarify the causes of the complicated peaks in the rocking curve. This approach is also effective for surface structural study using Auger excitation at selected atomic rows.