Dietary polyphenols are the most abundant antioxidants in daily diet and widely distributed in plants and plant-based foods, including vegetables, fruits, cereals, nuts, and beverages (e.g., tea, coffee, red wine). Over the past decades, there has been rising scientific interest in their diverse benefits to human health, since dietary polyphenols display various bioactivities, such as antioxidant activity, anti-inflammatory activity, anti-cancer, anti-microbial activity, neuro-protective activity, among others. Various studies have demonstrated that diet with polyphenols is strongly related to decrease the risk of chronic diseases. In this review, firstly, we systematically summarize classification and sources of dietary polyphenols, and focus on the current evidences defining their function and mechanism on improving chronic diseases, including diabetes, obesity, hypertension, hyperuricemia. Then, future directions of dietary polyphenols are discussed. Noteworthy, despite the physiological effects of dietary polyphenols have been widely convinced in vitro and in vivo, human trials show inconsistent evidence with their beneficial effects in chronic diseases administration, so as to their unclear molecular mechanism. More clinical studies are needed to provide clear evidence on dietary polyphenols against chronic diseases. In general, this paper provides comprehensive review of the sources and compositions of dietary polyphenols from plant materials, and presents an overview of the evidence on dietary polyphenols against chronic diseases, which may offer some constructive inspirations for further research on dietary polyphenols and industrial application in the food and medicine industry.