MicroRNAs (miRNA) have a significant role in the progression of gastric ulcer, and the sensitive and reliable detection of miRNAs is pivotal for the early diagnosis and treatment of gastrointestinal diseases. In this study, we developed a novel and efficient method for detecting miRNA-122, a crucial biomarker used to assess the prognosis of gastric ulcers. This method combines the bridge catalytic hairpin assembly (bCHA)-based target sequence recycling with the primer exchange reaction (PER), resulting in a highly sensitive and label-free approach. Specifically, the bridge CHA technique, which offers superior target recognition accuracy and increased signal amplification efficiency compared to the classic CHA procedure, can selectively identify the target miRNA and release the complementary sequence to serve as a primer to facilitate the PER. This PER process produces a large number of G-quadruplex sequences, which then bind with thioflavin T to significantly increase its fluorescence. This enhanced fluorescence is used to detect miRNA-122, with a detection limit as low as 3.12 fM. The proposed approach can achieve exact discrimination of the target miRNA-122. Due to its label-free character, high selectivity, and sensitivity, this technology can serve as a practical and universal approach for detecting different biomarkers in the early stages of gastrointestinal diseases.