Drug abuse directly endangers human health and social security, hence its sensitive and rapid detection is vitally important. In recent years, organic film-based fluorescent sensing technology has attracted more and more attention in the detection of drugs and explosives due to its advantages of simple operation and rapid detection. For film-based fluorescent sensors, in addition to sensitive materials, the surface morphology of the film is also an important factor affecting the performance. In previous studies, the regulation of surface morphology mainly depends on concentration changes or complex templates. Here, a novel fluorescent polymer probe was designed and synthesized, and a simple and efficient ultraviolet (UV)–ozone substrate treatment method is used to adjust their surface morphology. The results show that film has an excellent fluorescence enhancement effect upon exposure to methylphenethylamine (MPEA, a simulant of methamphetamine) vapor. The sensing effect of the film is significantly improved after UV–ozone substrate treatment, and the limit of detection was decreased by 10.4 times from 2.59 to 0.25 ppm. Further experiments show that the sensing performance of other fluorescent probe can also be improved by the UV–ozone substrate treatment. This convenient and general method may become a very effective approach to improve the performance of film-based fluorescent sensors.