SrRuO3 thin films were epitaxially grown on a (001) SrTiO3 substrate using pulsed laser deposition technique. Various defects such as V-grooves, threading dislocations and dislocation dipoles are observed in the SrRuO3 epitaxial film. It is found that the sidewalls of most V-grooves are {101} facets, and the dominant angle between the sidewalls is 90°. Some threading dislocations end at the apexes of the V-grooves while the others penetrate the entire film. The threading dislocations and V-grooves can partially relieve the strain in the epitaxial SrRuO3 film. During the relaxation process, a two-dimensional growth mode transforms into a three-dimensional one, along with the formation of mesa-like islands separated by V-grooves. The dimensions and distributions of V-grooves are associated with the growth conditions. The control of growth mechanism and surface morphology are very important for the fabrication of novel perovskite oxide devices.