We study a high-resolution melting (HRM) analysis method based on laser signal in self-made Fabry-Perot (FP) optical microcavity with high quality. We utilize the F-P optical microcavity as the micro-laser cavity, intercalated saturation dyes as the gain media and emitted laser signal as the detection signal to achieve high-resolution detection and screening of mismatched DNA by temperature scanning. We investigate on the melting curves of target DNA and mismatched DNA with 25 base-pairs and 50 base-pairs, respectively. Theoretical and experimental results indicate that the HRM detection method based on laser signal has lower melting temperature and higher signal-to-noise ratio.