Abstract: QM (Qilian Mountains) along the northeastern Tibetan Plateau are the main source of several important rivers, including the Shiyang, Heihe, and Shule rivers. Cloud microphysical properties are crucial for understanding the formation of precipitation. However, studies on the estimation of the cloud microphysical properties using aircraft measurements over the QM are limited. Herein, the cloud microphysical properties of a precipitating stratiform cloud event over the QM were investigated using the aircraft measurement data from KingAir-350 of the Weather Modification Office of Qinghai Province. The findings revealed that the precipitating stratiform event was primarily due to the terrain lifting of southerly airflow from the low topographic valley to the high mountain area. The maximum supercooled liquid water content in the orographic precipitating stratiform cloud was 1.13 g m⁻³. Moreover, the liquid water content was relatively high in low-altitude areas due to the presence of more water vapor. The formation and growth processes of ice particles varied at different altitudes in mountainous areas. At an altitude of 5600 m (−5.1°C), the formation and growth processes of ice particles are primarily dependent on the deposition and aggregation processes with weak riming process; at an altitude of 6560 m (−9.9°C), numerous aggregated ice particles were observed and spectrum broadening was obvious, indicating that the dominant formation and growth process for ice particles were deposition and aggregation processes; at an altitude of 7850 m (−17.0°C), almost ice phase particles were present with abundant aggregated dendritic ice particles, suggesting the dominant deposition and aggregation processes.