SrTiO3 surface was monitored in-situ by reflection high-energy electron diffraction(RHEED) during annealing and homoepitaxial growth in laser molecular beam epitaxy(LMBE). By analyzing RHEED pattern, we show the oscillation behavior of in-plane lattice constant and full-width at half maximum (FWHM) of diffraction streaks; the former is due to the interface between the annealed reconstruction surface and the growing film, and the origin of the latter is related to the relaxation of 2D islands by their edges. In addition, the phase shift of RHEED intensity oscillation was observed, due to plasma influence on the incident electron beam.