The invention discloses a phenylpyridine compound as shown in formula I and application thereof in preparing blood glucose reduction drug. (the formula is shown in the description), specifically, the invention discloses a phenylpyridine compound as shown in formula I or a salt of the phenylpyridine compound and application of the phenylpyridine compound in preparing drugs for treating and/or preventing non-insulin-dependent diabetes, high blood glucose or insulin resistance. The phenylpyridine compound and the salt thereof have a good inhibition effect for DPP-4 and have good market application prospect; and in addition, a novel direction is provided for the research and development of DPP-4.