The invention provides a nitrogen-containing double-tooth heterocyclic ring substituted tetrazole type rare-earth complex LnL3 expressed by the formula I, wherein Ar is a nitrogen-containing double-tooth heterocyclic ring; the center rare-earth ion Ln is any one of yttrium, lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium. The preparation method of the nitrogen-containing double-tooth heterocyclic ring substituted tetrazole type rare-earth complex LnL3 is characterized in that a nitrogen-containing double-tooth heterocyclic ring substituted tetrazole type three-tooth compound, namely a dipyridyl tetrazole type three-tooth compound or phenanthroline tetrazole type three-tooth compound, is taken as a single ligand, and simultaneously, coordination saturation is satisfied, and the tetrazole group in the complex serves as negative irons to realize electrically neutral charge balance together with center rare-earth metal cations. The obtained rare-earth complex is high in thermal stability, can be prepared into a device through an evaporation film-forming process or a solution film-forming process. Besides, the preparation method has the advantages of high yield, of the product has high purity, reaction time is short and operation is simple; and as a result, the cost is greatly reduced.