The invention relates to the field of triticum aestivum L. molecular breeding, and particularly discloses a triticum aestivum L. flag leaf length quantitative trait locus (QTL) linked molecular markerand application thereof. The single nucleotide polymorphism (SNP) molecular marker linked with triticum aestivum L. flag leaf length QTL QFll-5B is provided and located on a 5B chromosome long arm ofa RefSeqv1.0 genome edition, and is the 51st of a sequence shown in SEQ ID NO.31, polymorphism is C / T, and the SNP molecular marker can be obtained by amplification of a primer shown in a nucleotidesequence such as SEQ ID NO.1-3. The SNP molecular marker can accurately trace the triticum aestivum L. flag leaf length QTL QFll-5B, and predict the flag leaf length characteristics of triticum aestivum L., and molecular design breeding is convenient. The invention further discloses a method for identifying the molecular marker. The prediction accuracy of the flag leaf length can be enhanced by using the method, so that varieties or strains of the triticum aestivum L. with increased the flag leaf length are conveniently and rapidly screened for breeding, and the breeding progress of the varieties of the triticum aestivum L. with a high yield can be greatly accelerated.