Located in the northeastern Tibetan Plateau, the Qilian Mountains（QM）are the main source of several important rivers including the Shiyang, Heihe and Shule rivers. The cloud microphysical properties have a critical role in understanding the precipitation formation. However, the aircraft measurements on the cloud microphysical properties over the QM are few. By using the aircraft measurement data of KingAir-350 of the Weather Modification Office of Qinghai Province, the cloud microphysical properties of a precipitating stratiform cloud event over the QM was investigated. The results show that the formation of the precipitating stratiform event was primarily produced by the terrain lifting of nearly southerly airflow from the low topographic valley area to high mountain area. The maximum supercooled liquid water content in the orographic precipitating stratiform cloud was 1.13 g m-3. The liquid water content was relatively high in low-altitude areas due to the existence of more water vapor. The formation and growth processes of ice particles varied at different altitudes in mountainous areas. At the level of 5600 m (-5.1 ℃), the formation and growth processes of ice particles primarily depended on deposition and aggregation processes with weak riming process; at the level of 6560 m (-9.9 ℃), a large number of aggregated ice particles were observed and the spectrum broadening was obvious, indicating that the dominant formation and growth process for ice particles were deposition and aggregation processes; at 7850 m (-17.0 ℃), there were almost ice phase particles with abundant aggregated dendritic ice particles, indicating that the deposition and aggregation processes were dominant at this high altitude.