Abstract: Stratiform clouds with embedded convection (SEC), with convective clouds embedded within stratiform clouds, exhibit significant catalytic potential, making them the main targets for artificial rain enhancement. Widespread agricultural drought and the pressing need for water conservation in North China necessitate research on artificial precipitation enhancement in the region’s cloud systems. This study coupled the weather research and forecasting model with a silver iodide (AgI) seeding parameterization scheme to simulate aircraft AgI seeding during a SEC precipitation event in northern Shanxi on 16 June 2021. The simulation results were validated against satellite and airborne cloud physics observations. Given the good agreement between the cloud top temperature and liquid water content, the catalytic precipitation process was simulated using the actual seeding trajectory and dosage. The simulation results indicated that the seeding operation significantly enhanced precipitation, with local cumulative increases of 15–20 mm and a regional average enhancement rate of 9.6%. AgI nucleation was primarily dominated by deposition nucleation, followed by condensation–freezing nucleation, with immersion–freezing nucleation being the weakest mechanism. Direct AgI seeding increased the ice crystal concentration of the cloud, and the resulting water vapor consumption inhibited snow and graupel production and growth in the early stage. The subsequent conversion of ice crystals to snow, followed by the collision of snow with cloud droplets to form graupel, increased the total snow and graupel concentrations. More snow and graupel particles fell below the 0°C level, melting into large raindrops. This enhanced the cloud–rain collision process, ultimately increasing surface precipitation. Quantitative analysis of the seeding-catalyzed microphysical processes showed that AgI seeding enhanced snow and graupel melting by 27.26% and 20.53%, respectively, compared with natural clouds, confirming that these intensified melting rates were the main microphysical processes affected by seeding, which influenced precipitation increase. These results reveal and quantify the mechanisms of seeding-influenced precipitation and cloud microphysical structure, enhancing the understanding of the physical mechanisms of artificial catalytic mixed cloud precipitation enhancement and providing valuable references for artificial influences on cold cloud weather operations in Northern China.