The invention provides a compound, and a synthetic method and application thereof. The compound comprises a [Ga3PQ8]n<2n-> anionic group, wherein Q=S or Se, and n=1 or 2 or 3 or 4. The synthetic method comprises proportioning gallium, phosphorus, Q (Q=S or Se), AX (A=Na or K or Rb or Cs, X=F or Cl or Br or I), uniformly mixing the raw materials, putting in a quartz tube, performing vacuum-pumping, sealing the tube, putting in a muffle furnace, slowly heating to 600-900 DEG C, keeping warm for at least 1 hour, extinguishing the muffle furnace, and naturally cooling to room temperature, so as to obtain the compound. The compound is a colorless or yellow crystal or powder, possesses excellent infrared nonlinear optical performances and extremely high laser damage threshold. The synthetic method is simple in steps, and the obtained product is high in purity, high in yield and suitable for commercialized production.