Tartary buckwheat (Fagopyrum tataricum) sprouts is a newly healthy food. Tartary buckwheat sprouts were treated with different photoperiod (0, 4, 8, 12, 16 and 20 h·d^-1). The biomass, the contents of chlorophyll and main nutritional components, and the expression level of genes related to flavonoids synthesis were measured in order to clarify the mechanism of the effect of different photoperiod on the quality of Tartary buckwheat sprouts, the results showed that: (1) with the increase of growth time of Tartary buckwheat sprouts, the biomass of Tartary buckwheat sprouts increased as a whole, and the growth state of sprouts was the best and the fresh weight was the highest at 16 h·d^-1 photoperiod. (2) The effects of different photoperiod on the contents of nutrients in Tartary buckwheat sprouts were different. The content of soluble sugar began to decrease gradually on the second day of germination, and the content after 10 days was only 13.5% and 14.5% of that on the second day. The anthocyanin content was the highest (2.16 mg·g^-1) when the photoperiod was 12 h·d^-1 on the second day of sprouting, and decreased after 4 to 10 days of different photoperiod treatments. Rutin is the main flavonoids in Tartary buckwheat sprouts. The content of rutin changed after different photoperiod treatments, and proper light was beneficial to its synthesis and accumulation. The highest content (59.60 mg·g^-1) was obtained when the photoperiod was 16 h·d^-1 on the 4th day of treatment. (3) qRTPCR analysis showed that the expression of flavonoids synthesis related genes in Tartary buckwheat sprouts treated with different photoperiod was the highest on the second day, and decreased with the growth cycle. However, the expression of the key enzyme gene FtFLS1 and the anthocyanin branch gene FtDFR2 increased, and showed strong lightinduced characteristics. The results showed that photoperiod had a great effect on the biomass of Tartary buckwheat sprouts, darkness was beneficial to Hypocotyl elongation, and long photoperiod (16 h·d^-1) was beneficial to the increase of fresh weight. During the germination of Tartary buckwheat, the contents of soluble sugar, anthocyanin and rutin in Tartary buckwheat sprouts decreased as a whole, and the contents of soluble sugar and anthocyanin were the highest on the second day when the photoperiod was 16 h·d^-1. The content of rutin was the highest on the 4th day after treatment when the photoperiod was 16 h·d^-1. It was suggested that Tartary buckwheat sprouts should be fed at 16 h·d^-1 for 4 days.