Abstract: Based on the observation data obtained by the “Rainfall Enhancement and Hail Suppression Project on the Eastern Side of Taihang Mountains” in this paper, we analyze the microphysical characteristics of the stratiform cloud induced by the upper-level westerly trough on May 21, 2018. The results indicate that the supercooled liquid water content in the −5°C layer is less than 0.05 g m⁻³, and the concentrations of supercooled cloud droplets range from 10–10² L⁻¹. Needle-like and columnar ice crystals are often observed in regions with high number concentrations of ice crystals, which may be related to ice crystal fragments produced by the Hallett–Mossop mechanism and other mechanisms, which are then deposited under super-saturated ice conditions. Ice crystal habits are predominantly planar and dendritic in regions with low ice-crystal number concentrations. Ice and snow crystals mainly grow via deposition and coalescence processes, with a weak rimming process. The liquid water content accounts for more than 70% in regions with a peak cloud water content near the 0°C layer. These particles are mainly cloud droplets with diameters ranging from 10 μm to 50 μm, accompanied by a few aggregates. The supercooled water content is about 0.05 g m⁻³ in other regions near the 0°C layer, with the ice crystal habits being predominantly aggregates, rimed snow, and graupel. Most of the particles are spherical droplets and melting ice crystals in the liquid water layer. Vertical observations indicate that the ice- and snow-crystal number concentrations increase with height above the 0°C layer. The supercooled-liquid-water content of the mixed layer is much lower in a stable stratiform cloud. Most particles mainly grow by deposition and coalescence, and the degree of ice crystallization is much higher. The existence of liquid droplets indicates that the transformation between the liquid and ice phases is not sufficient in strongly developed stratiform cloud regions where supercooled liquid water is relatively abundant. The particle size distributions at different temperature levels indicate that the average number concentration of ice particles in regions with an abundant supercooled-liquid-water content is higher than those with a low supercooled-liquid-water content. However, the average diameter of ice particles in regions with low supercooled-liquid-water content is larger.