Abstract: The hypocenter and origin time of the MW7.9 Wenchuan earthquake of May 12, 2008, were relocated precisely using the observation data from both of the Sichuan Province Seismic Network and the Zhipinpu Reservoir Seismic Network. It is pointed out that the factors affected significantly to the precise and accurate determination of the hypocenter and origin time of the great earthquakes such as the Wenchuan earthquake are the limitation of far stations, incompleteness of the crust model used for earthquake location, and the inconsistency existed in the direct P phases detected from the near-by seismic stations and the far stations being generated from different rupture areas and at different times. To diminish the limitation caused by these factors, data from the local seismic stations were analyzed, and from these stations, 15 near-by stations of epicentral distance of 5mdash;160 km, with well azimuthal distribution, and with accurately correlated direct P phases were selected for inversion. The preferred relocated source parameters, obtained from inversion, have coordinates latitude 31.018deg;Nplusmn;0.3 km, longitude 103.365deg;Eplusmn;0.3 km, focal depth 15.5 kmplusmn;0.3km, origin time (Beijing Time) May 12, 2008, 14:27:57.59plusmn;0.03 s.