The invention discloses a promoter 6M3B and applications of the promoter 6M3B. The promoter provided by the invention is named as 6M3B, and is DNA molecules shown by the nucleotide from the 7th site to the 94th site of the 5' terminal in the sequence 1 of the sequence table. The invention also protects the DNA molecules (fusion genes), sequentially comprising the DNA molecules shown by the nucleotide from the 7th site to the 94th site of the 5' terminal in the sequence 1 of the sequence table and reporter genes from the upstream to the downstream. The invention also protects recombinant plasmids containing the fusion DNA. The invention further protects recombinant bacteria obtained by importing the recombinant plasmids into host bacteria. The invention also protects the applications of the recombinant bacteria in detecting 2,4,6-trinitrotoluene and/or 2,6-dinitrotoluene and/or methylbenzene. A biosensor provided by the invention can be used for detecting and identifying the position of the explosive, such as the mine during the wartime and after the war, and moreover, a novel method is provided for detecting TNT in the soil and the water environment.