In this paper, we demonstrate a miniaturized nanofiber methane sensor based on tunable diode laser absorption spectroscopy (TDLAS). Based on the Beer-Lambert law, we chose a methane absorption line near 1.6 μm, performed a wavelength modulation on a distributed feedback diode laser (DFB-DL), used a lock-in amplifier to demodulate the second harmonic signal, and established a complete TDLAS system based on nanofiber. The system is used to examine the influence of different incident powers and pressures on the second harmonic signal at room temperature. We obtain the system’s pressure broadening and frequency shift coefficients through experiments. It is found that nanofibers with a smaller diameter can produce stronger absorption for methane. Moreover, the designed nanofiber sensor is a powerful tool for tracing gas measurements under low power conditions and has considerable application potential in gas species and quantitative analyses.