Two-dimensional (2D) ferroelectrics usually exhibit instability or a tendency toward degradation when exposed to the ambient atmosphere, and the mechanism behind this phenomenon remains unclear. To unravel this affection mechanism, we have undertaken an investigation utilizing NH and two-dimensional ferroelectric SnS. Herein, the adsorption and desorption of NH molecules can reversibly modulate the electrical properties of SnS, encompassing I-V curves and transfer curves. The response time for NH adsorption is approximately 1.12 s, which is much quicker than that observed in other two-dimensional materials. KPFM characterizations indicate that air molecules' adsorption alters the surface potentials of SiO, SnS, metal electrodes, and contacts with minimal impact on the electrode contact surface potential. Upon the adsorption of NH molecules or air molecules, the hole concentration within the device decreases. These findings elucidate the adsorption mechanism of NH molecules on SnS, potentially fostering the advancement of rapid gas sensing applications utilizing two-dimensional ferroelectrics.