Carbon nanotubes (CNTs) were directly grown on nickel substrates by low pressure chemical vapor deposition (LPCVD) using acetylene-hydrogen as precursor. The reaction temperature was in the range of 500～800 ℃. Temperature effects on the growth and morphology of CNTs and their field emission properties were investigated. The growth rate of CNTs increased first with temperature increase from 500 ℃, and reached a maximal value at 650 ℃, then decreased when the temperature increased further. The morphologies and structures of deposited CNTs were characterized by scanning electron microscope and Raman spectroscopy. The diameter, length, uniformity and crystallinity of the deposited CNT also showed a temperature dependence. The field emission properties of the CNTs were tested, the field emission principle was studied deeply, and the results proved the temperature dependence of CNTs properties and the existance of optimization of temperature. The experimental result indicated that the morphology, structure and field emission properties of CNTs could be controlled by the reaction temperature in a certain range.