A study of Si, GexSi1-x growth mode on H-terminated vicinal Si substrate by RHEED is presented. About 10 nm Si epilayer is required to obtain a smooth Si substrate. Bi-atomic terrace dominate on the stable surface both of Si and GexSi1-x single atomic terrace is present in the mean time. Dimer row on bi-atomic Si terrace is perpendicular to terrace edge while dimer row on GexSi1-x bi-atomic terrace is paraller to it (90°rotation). GexSi1-x bi-atomic terrace edge is more straight than Si one.