ZnO nanostructures were prepared by chemical vapor deposition (CVD) in a double-tube furnace. The effects of the carrier gas and oxygen flow rates on the morphology and yield of the products are described. The concentration distributions of O-2 and Zn vapor were simulated by the computational fluid dynamics (CFD) software FLUENT. The experimental and simulation results revealed that the content of Zn was much greater than that of O-2 at different deposition positions and that the deposition reaction was mainly controlled by the O-2 concentration. The reaction occurred mainly on the outside of the inner tube with the increasing N-2 flow. In contrast, the reaction occurred mainly on the inside of the inner tube with the increasing O-2 flow. A reduction of the carrier gas flow rate and an increase of the O-2 flow rate were both conducive to a morphology transition of the ZnO nanostructure from needle-like tetrapodal to nail-like tetrapodal.