The contents of total flavonoids in leaves of Lycium barbarum L. at different picked times were determined by RP-HPLC. It was showed that the content of total flavonoids in leaves was the highest(1.99%) in May and the second(1.36%) in August, and decreased sharply after September and went down to the lowest in October(0.36%).So the best picked time in Xi′ning City, Qinghai Province was early summer. Moreover, contents of three major aglycones, such as quercetin, kaempferol and is orhamntin, were compared. Consistently for all picked times, the content of quercetin was much higher than those of kaempferol and isorhamntin.