A novel compound and an application thereof as a flame retardant are disclosed. An infrared spectrum of the compound has characteristic absorption peaks at 3336 cm<-1>, 1640 cm<-1>, 1465 cm<-1>, 1230 cm<-1>, 1126 cm<-1>, 1022 cm<-1> and 848 cm<-1>. The compound is prepared by adopting pentaerythritol diphosphate dichloride and magnesium hydroxide as raw materials, adopting anhydrous acetonitrile as a solvent and adopting anhydrous aluminum trichloride as a catalyst. The compound can be used as a flame retardant of a polymer material, the using amount of the compound is low, the polymer material to which the compound is added is low in smoke generating amount and good in mechanical performance, and the compound is superior to flame retardants at present.