In order to investigate the effects of olfactory training vary by duration, the same testing method was performed over a period of 6 years. In total 111 patients were included on this experiment. The result shows that the recovery of olfactory function improved dramatically in the first 16 weeks, after that period, the patients began to recover in a slower pace. Overall, the olfactory training can improve the patients' olfactory functions continuously over a long period.