In this study, a two-zone furnace had been used to grow ZnO nanowires (NWs) on Si (100) substrates by thermal evaporation method via the vapor-solid (VS) mechanism. We mixed zinc oxide powder and graphite powder as source. By controlling the growth temperature, source temperature, growth pressure, source amount, growth time, growth position and carrier gas, ZnO NWs had been grown a variety of condition. When growth temperature was set at 500 ^oC, ZnO were grown disorderly. Nanobelts and nanowires were grown simultaneously on silicon substrate. As growth temperature increasing to 700 ^oC, uniform ZnO NWs had been grown with 10-20 μm in length and 80-100 nm in diameter. But when growth temperature was increased continuously to 900 ^oC, the silicon substrate didn’t have ZnO NWs trace. Not only growth temperature but also other parameters had a lot of influences on growing ZnO NWs. Such as source amount, it mainly affects nanowire’s morphology and density of nanowires. Source temperature affects the source vapor pressure to adjust the atmosphere in tube. Growth time was related to the length of ZnO NWs. The position was associated with the deposit of source vapor. Therefore, we can grow appropriate ZnO NWs to increase the diversity of the research on electrical application part in the future. ZnO NWs were characterized by field-emission scanning electron microscope (FE-SEM), x-ray diffractometer (XRD), and transmission electron microscope (TEM) about the morphology and crystal structure.