Gold nanoparticles are prepared in chloroauric acid trihydrate (HAuCl4·3H2O) aqueous solution by the ablation with a focused femtosecond pulse laser beam of 800 nm wavelength and 30 fs pulse duration. The effects of HAuCl4·3H2O aqueous solution concentration, laser pulse energy and dispersant polyvinyl pyrrolidone (PVP) amount on particle size and size distribution of gold nanoparticles are investigated by means of UV-Vis absorption spectrum, transmission electron microscopic morphology, X-ray diffraction spectrum, and selected area electron diffraction pattern. The results show that the surface plasma resonance absorption peak of the gold nanoparticles locates around 530 nm. Lower solution concentration, higher laser pulse energy and higher PVP amount are helpful to obtain nanoparticles with smaller average particle size, narrower particle size range and higher dispersion when other experimental parameters are fixed at certain values. The prepared particles are mostly spherical and display multi-nanocrystal surface structure. The strong X-ray diffraction peaks of (111), (200), (220) and (311) crystal planes of gold nanocrystal are observed. The growth process of gold nanoparticle includes aggregation stage and adsorption stage.