A flask solvothermal method was firstly utilized to facile synthesize greigite Fe3S4 micro-crystals (MCs). By using iron nitrate, element sulfur as raw materials as well as oleylamine as the solvent, high yield of Fe3S4 MCs with hexahedron microstructure was obtained. In addition, it was found that it was easily to achieve transformation between Fe3S4 and Fe7S8 through changing reaction temperatures and iron-sulfur ratios. The several different morphologies of Fe3S4 MCs were obtained by using other sulfur sources. The synthetic approach demonstrated here could be of great potential for the controlled synthesis of other metal chalcogenides.