At present, more and more attention has been paid to the detection of common explosives trinitrotoluene (TNT). In this study, a low-cost fluorene-based green-emitting conjugated polymer (FGEP) is used to develop a fluorescence quenching sensor for the detection of TNT. The quenching efficiency of TNT by different thickness FGEP films at different solution concentrations is studied experimentally. The experimental results show that the quenching efficiency of the sample film with a concentration of 0.5 mg/mL (thickness of 19.50 nm) in TNT vapor reaches the maximum of 71.71%. Based on the study of the sample film with the highest quenching efficiency, it is found that the film has good reversibility to TNT, and when the excitation light intensity is 16.5 mW, the fluorescence quenching efficiency is the best. Finally, the experimental study of the samples under the action of TNT and photobleaching is carried out. The research results provide a basis for the subsequent realization of a low-cost, easy-to-prepare, highly repeatable and engineering-friendly explosive sensor.