Abstract: Ya'an Tibetan tea is a kind of dark tea. It was reported that Ya'an Tibetan tea had less alerted effects and does not affect people'sleep. Caffeine is the major alkaloid in tea and acts as a central nervous system stimulant.Therefore,20 Ya'an Tibetan tea samples had been taken as study materials,and the dark tea samples from other regions of China and other types of Chinese traditional teas had been taken as contrast materials.Using high performance liquid chromatography( HPLC) method for different samples of tea to detect the content of caffeine.It had discussed that the relationship between Ya'an Tibetan tea does not affect people'sleep and the caffeine content.Results showed that the caffeine contents range of 20 Ya'an Tibetan tea samples were 1.99% ~3.64%,and the average content was 2.88%. The caffeine contents range of other types of Chinese traditional tea samples except oolong tea were 3.46% ~ 4.00%,and it showed that the caffeine content of Ya'an Tibetan tea samples were at low level.There was difference about the content of caffeine in dark tea among different regions of China.Results showed that the order of average caffeine contents was Liu Pao tea > Puerh ripe tea > Ya'an Tibetan tea,the caffeine content of Fangbao tea was the lowest.The main reasons that Ya'an Tibetan tea does not affect people'sleep were as follows: the material maturity of Ya'an Tibetan tea was higher,and the caffeine content of manufactured Ya'an Tibetan tea was lower. The caffeine content could be reduced by the special manufacturing process of Ya'an Tibetan tea.It could speculate that the content of combined caffeine was high in Ya'an Tibetan tea.The results wouldl provide helpful information for the quality controls and the study on the mechanism of the Ya'an Tibetan tea did not affect people'sleep.