The goal of the article is to definite that sleep with sufficient time and depth is a high quality sleep regardless of whether the sleep time changes or not. The author had conducted an experiment about sleep time. During the experiment, the author changed participants’ main sleep time four times. The result of the survey shows that participants take a few days to adapt to the new condition after their main sleep times have changed. It would not affect the recovery of the energy of the people even though the time point of their main sleep changes.