Twodimensional diamond (2DD) is an atomically thick diamond film having unique characteristics with retaining intrinsic properties of bulk diamonds. Currently, researches on 2DD mainly focus on theoretical investigations of structure, functionalization, and electrical properties, while a few of experimental works are reported on preparation. In this paper, the theoretical and experimental progresses of structure, surface functional modulation and electrical properties of 2DD are briefly reviewed dependent on atomic thickness (layer number), and the development trends, challenges, and potential applications are discussed.