To meet the needs of monitoring CH₄ gas concentration in coal mines and gas fields， a frequency modulated spectral system based on near-infrared distributed feedback lasers was built for rapid measurement of high concentration methane. The system obtained the optimal modulation frequency range and the optimal signal-to-noise ratio of the absorption component through simulation optimization and experimentation. When the modulation frequency is 353 MHz， the power is 25.08 mW， and the effective optical path is 0.6 m， a CH₄ absorption spectral line of 6 046.83 cm^-1 is selected to achieve 1 Hz CH₄ gas concentration detection. The amplitude of the frequency modulation absorption component signal has a linear relationship with concentration， with a linearity error of 2.88% and a linear fitting coefficient R² of 0.997 4. For standard CH₄ gas with a volume fraction of 2%， the relative error is less than 1.3‰. When the integration time is 1 s， the Allen variance is 4.032 1 ppmv. When the integration time is 347 s， the Allen variance is 0.222 8 ppmv， and the detection sensitivity is 2.28 × 10^-7， which meets the measurement requirements for high-speed and highly sensitive CH₄ gas. The experimental results indicate that frequency modulation spectroscopy technology has broad application prospects in low detection limit and high sensitivity gas sensing.