Reflection high energy electron diffraction (RHEED) intensity oscillations were observed during molecular beam epitaxy (MBE) growth of Ge on Si(111) surface. At 250 degrees C the oscillations continue up to 6 monolayers. The intensity of the reflected beam is calculated by solving the one-dimensional Schrodinger equation. Monte-Carlo simulation was used for the growth simulation in order to investigate fundamental behaviours of reflectivity chan during the Stranski-Krastanov growth of Ge on the Si(111) surface at 250 degrees C.