Screening for BRCA2 gene mutations is clinically important for breast cancer risk assessment, morbidity detection, early diagnosis and gene therapy. Most existing breast cancer gene sensing assays require complex processing, high cost and weak recognition of single-base mutations. To simplify the process of gene-sensor preparation and improve its application possibility, the article realized the detection of BRCA2 in one step through the design of DNA molecular hairpin structure. The molecular hairpin stem contains BRCA2 complementary sequences, and the stem-loop junction is labeled with a tetramethylrhodamine fluorescent group. The target gene can be measured in one step. The optimized experimental results showed that the sensors detection range was different when the concentration of molecular hairpin was different. The linear detection range of BRCA2 was 1~50 nmol·L-1 at 150 nmol·L-1, 1~100 and 1~200 nmol·L-1 at 300 and 600 nmol·L-1, respectively, and the detection limits for the three concentrations were 0.54, 0.72, and 1.81 nmol·L-1, respectively. In addition, the specificity of the sensor for detecting BRCA2 was outstanding, especially for identifying single-base mutations. The method is simple and specific and can be used not only for early screening of breast cancer in high-risk groups but also for other types of genetic tests, providing a new method with simple preparation and convenient operation for applying genetic sensors.