Using a selective laser melting (SLM) machine-dimetal 240, a series of experiments for direct manufacturing of precision metal parts were carried out. Some effect factors on precision deposition layer by layer were studied combining with the experiments. They can be divided into three categories: hardware, software and materials. Hardware factors include the beam quality, power and wavelength of the laser, the focusing performance of the optical system, and the scan speed and the powder delivering precision. Software factors mainly include the designing of the metal parts with CAD software, slicing of the CAD model and scan strategies. Material factors are the composition of the material, the melting point, and the shape and the size of the metal particle. CAD models will be manufactured into metal parts by using metal powders with different composition and particle size layer by layer. The analysis shows the parts are metallurgical bonded entities with density of 100%, dimension precision <0.1 mm and surface roughness of about 30 μm.