the present invention discloses an active - hydrogen - containing phosphorus compound for cross - linking a resin and for imparting flame - retardancy to the cured resin , and in particular to a cured frame - retardant epoxy resin prepared by reacting the hardener with a di - or poly - functional epoxy resin via an addition reaction between the active hydrogen and the epoxide group . the present invention also discloses an epoxy resin made from the active - hydrogen - containing phosphorus compound and epihalohydrin .