Abstract: The processing conditions under which the rutile single crystal grows by way of flame fusion were studied comparing its growth and annealing results in different atmospheres. The results showed that the oven atmosphere is decisive to whether crystal could be formed or not, which may be controlled by the ratio of hydrogen to oxygen supplied in it. The crystal is easy to grow in a wide growth rate range to become a relatively big one if the oven atmosphere is suitable. It was revealed that no complete crystal can be obtained relying simply on adjusting (increasing or decreasing) the growth rate. The oven atmosphere in which the oxygen partial pressure is higher than oxygen's dissociation pressure at the liquid-solid interface is proved a prerequisite condition to form a complete crystal. The role of annealing is to relieve thermal stress formed in crystal growth but more important, it shall eliminate oxygen vacancies by oxidization reaction. The annealing time can be considerably shortened in an oxygen atmosphere in which a transparent light yellow rutile single crystal is obtained as its natural color.