Using the mesoscale model MM5V3.6 and the NCEP daily reanalysis data every 6 hours,we numerically simulate the snowstorm on March 1—2,2003 in Liaoning Province.We emphatically analyze and discuss the genesis,development and evolution characters of the mesoscale system during this course.Through the simulation we find that the MM5V3.6 has the ability to successfully simulate each factor in this mesoscale snowstorm.The results show that the convergence of low level air flows and the divergence of upper air flows resut in the strengthening of ascending motion and the genesis and maintenance of the center of low level positive vorticity,therefore the water vapor condensation in the vertical direction is the gensis mechanism of the snowstorm.