A snowfall process in Qilian mountains during 7~8 February 2006 is simulated using the mesoscale model MM5V3. Seeding tests are made in order to study the effects of adding artificial ice particlesto the snowfall. Tests of different seeding amounts and seeding heights are conducted. The changes of the microphysical processes and thermal and dynamical processes are analyzed. Results show: The seeding area is in the upwind of snowfall center with the supercooled water. After seeding, the precipitation increases at snowfall center and decreases aroundthe center. It is to increase more snowfall if seeding in the levels of more supercooled water and less ice particles. The vapour and supercooled water are depleted to increase ice and snow. The collection of ice by snow, the conversion of ice to snow and the deposition of snow are the main sources of snow. The changes of microphysical phases release more latent heat which results in warming the atmosphere andstrengthening the updraft. At the same time these changes affect the vertical velocity and hydrometers surrounding the snowfall center. The updraft become weaker and snow become less which produces the decrease snowfall area.