With the continuous expansion of flame retardant materials application and accordant new environmental regulations, boron-based flame retardants have attracted more and more attention due to their characteristics of high efficiency, low toxicity, environmental protection, and effective smoke suppression. In this paper, the application research and the latest progress of inorganic boron flame retardants, organic boron flame retardants and multi-component boron flame retardants in polymer flame retardancy were reviewed. The flame retardant mechanism, action mode of different boron flame retardants and application progress of boron-based flame retardants in different polymer systems were mainly discussed. In particular, two effective flame retardant mechanisms of boron-based flame retardants were introduced, namely the acid-catalyzed flame retardant mechanism of boron phosphate (BP) and nano-blocking flame retardant mechanism of surface modified boron nitride nanosheets (BNNS). As for the development trend of boron-based flame retardants, the nano-scale, microencapsulation and multifunctional surface modification of inorganic boron-based flame retardants could be the key directions of their future development; while organic boron based flame retardants tend to be multi-elemental, including boron, phosphorus, silicon and other elements, to improve their water resistance, and achieve high-efficiency flame retardant through multi-element synergistic effect.