ZnO nanowires with the diameter of 50 similar to 100 nm and length up to several tens of microns were fabricated on Au coated Si or sapphire substrates by the reaction between ZnO and graphite powder through the chemical vapor transport (CVT) method. The FESEM, HRTEM and SAED results confirmed that the individual nanowire has the nature of single crystal and the  crystal orientation is observed from a ZnO nanowire. New experimental evidences have been provided for the initial and final growth states to support the VLS mechanism for nanowire growth, and a growth mechanism of binary oxide nanowire proposed in the course of studying the growth process of ZnO nanowires systematically. It is considered that the Zn vapor formed by carbothermal reduction is transported to, and reacts with, the Au cluster catalysts on substrates to form Au-Zn alloy droplets. As the droplets become supersaturated by Zn vapor, the extra Zn segregates backward and reacts with the trace of oxygen in the reactor or the oxygen sources produced during the carbothermal reaction to form crystalline ZnO nanowires. The spontaneous growth of a large quantity of nanowires reduces the concentration of Zn in the alloy droplets, which may lead to the termination of nanowire growth.