Tartary buckwheat has become popular healthful food due to its antidiabetic and antioxidant activities. In the current study, the in-vitro α-glucosidase inhibitory and antioxidative activities of different parts of Tartary buckwheat were evaluated throughout the growth stages. In addition, the phytochemical profiles and quantitative analysis were further achieved by HPLC-DAD. Tartary buckwheat root extracts at a concentration of 0.5 mg/mL showed significant inhibition more than 80% in the flowering and yield stage, while acarbose was 87.4% inhibition at 5 mg/mL. It also showed good antioxidant capacity using 2,2-diphenyl-1-picryl-hydrazyl, 2, 2ʹ-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt, and ferric reducing antioxidant power determination. The antioxidant capacities of roots ranged from 128 to 158 μM VC, from 226 to 409 μM VC, and from 77 to 205 μM butylated hydroxytoluene (BHT) (equaling VC or BHT per 1 g of dry weight), respectively. Chemical composition analysis showed that the leaf contained more rutin and the root more phenylpropanoid. The results may provide a better understanding of the variation of Tartary buckwheat as a functional food for preventing diabetes and antioxidant.