Abstract: From April 16 to 21, 2024, Qinghai Province experienced a precipitation process, with the rainfalls mainly concentrated in the eastern part of Qinghai. 8 national meteorological stations recorded daily precipitation exceeding their extreme thresholds. Based on observational data from China's national surface meteorological stations and ERA5 reanalysis data, this study examines this extreme precipitation event, revealing its evolution from the perspective of ageostrophic motion by the moist C-vector. Results show that this precipitation process occurred on the south side of the entrance region of the 200 hPa upper-level jet stream and ahead of the trough associated with the 500 hPa Tibetan Plateau vortex, featuring a long duration, high intensity, and rapid development and decay. Diagnosis based on the moist C-vector reveals that within the key precipitation area, the ascending motion forced by diabatic heating from moisture uplift and condensation is mainly located in the lower troposphere, driving the occurrence of extreme precipitation. While the descending motion, forced by adiabatic effects, prevailed in the upper troposphere at the same time. The ascending motion in the upper troposphere is driven by the adiabatic effect of the upper-level jet, leading to rapid development of the precipitation. The plateau vortex develops rapidly due to the diabatic heating effect of moisture condensation, exciting a zonal secondary circulation, whose descending branch affects the key precipitation area, causing rapid decay of the extreme precipitation; the northward development and shift of the upper-level jet remove the favorable conditions for adiabatic suction in the upper troposphere, ultimately ending the extreme precipitation. The study reveals the process of the adiabatic and diabatic effects driving the precipitation based on the perspective of the ageostrophic motion, and quantifies the contribution of the above two. The potential forewarning value of the moist C-vector is also discovered, providing a reference for further exploring its application in the future.