In summer 2011, a warm cloud modification experiment was performed by the Beijing Weather Modification Office. Cumulus humilis over the Great Wall at Beijing Badaling was selected as the seeding target cloud, and hygroscopic flares were ignited at the cloud base level. Seeding and in-situ observations were conducted by a Y-12 aircraft equipped with a seeding device and cloud physics probes. Different strategies were used in an experiment on 1 June. A microphysical response consistent with the warm cloud seeding conceptual model was observed after seeding. The plume of the flare was subsequently measured in a clear zone, and the particle size distribution of the hygroscopic flare was illustrated.