It is essential to monitor continuously the concentration of H2 S in the procedure of natural gas desulfurization. The design of monitoring system based on the laser absorption spectroscopy to measure H2 S in desulfurization was presented. In order to realize high sensitive measurement, the compact Herriot multi reflection gas absorption cell was developed, which is placed near the desulfurization tower. The detection system is characterized by signal of detector transferred directly to the analysis room. The experiments were carried out in the gas gathering station in Shandong Province. The results show that the detection limit is 300 ppb and the operation is stable and reliable. All the results demonstrate that the system satisfies the demand of monitoring H2 S in the procedure of natural gas desulfurization.