Nitraria tangutorum Bobr. (NTB), mainly distributed in the Qaidam Basin of Tibetan Plateau, have high economic, ecological and medicinal value. The chemical compositions in the NTB fruits were tentatively analyzed and characterized by applying UPLC-Q-TOF-MS/MS. Total 45 constituents, including 9 hydroxycinnamic acids derivatives, 12 flavonols, 4 flavonoids, 1 trolox derivative, 8 beta-carboline alkaloids, 4 tryptophan derivatives, and 7 other amino acid derivatives were identified by comparing with standard products, and analyzing their retention times, characteristic fragment ions and deprotonated molecule ions. The activity studies in vitro indicated that NTB-Z and NTB-C extracts had marked inhibitory effects against sucrase and maltase. Further sucrose/maltose/starch tolerance experiment demonstrated that both NTB-Z and NTB-C extracts at 400 mg/kg could markedly lower the postprandial blood glucose (PBG) level in diabetic animals. All these results indicated that the NTB fruits could be used as the functional health food or medicine for controlling postprandial blood glucose level.