An optical hydrogen sulfide (H2S) sensor based on wavelength modulation spectroscopy with the second harmonic (2f) corrected by the first harmonic (1f) signal (WMS-2f/1f) is developed using a distributed feedback (DFB) laser emitting at 1.578 μm and a homemade gas cell with 1-m-long optical path length. The novel sensor is constructed by an electrical cabinet and an optical reflecting and receiving end. The DFB laser is employed for targeting a strong H₂S line at 6 336.62 cm^-1in the fundamental absorption band of H₂S. The sensor performance, including the minimum detection limit and the stability, can be improved by reducing the laser intensity drift and common mode noise by means of the WMS-2f/1f technique. The experimental results indicate that the linearity and response time of the sensor are 0.999 26 and 6 s (in concentration range of 15.2—45.6 mg/m³), respectively. The maximum relative deviation for continuous detection (60 min) of 30.4 mg/m³H₂S is 0.48% and the minimum detection limit obtained by Allan variance is 79 μg/m³with optimal integration time of 32 s. The optical H₂S sensor can be applied to environmental monitoring and industrial production, and it has significance for real-time online detection in many fields.