The airflow distribution and law of muzzle flow field during the dynamic launching of electromagnetic rail launcher are studied. A two-dimensional transient model of projectile under high Mach number is established based on overlapping multi-block structured mesh,DFBI and Java program. The unsteady numerical method and the reliability of data interaction are validated by taking double ellipsoid model as the object of study. The flow fields in the dynamic launching processes of four cases are simulated. The numerical results show that the complex flow fields due to the interaction of projectile nose shock wave,spherical shock wave with moving center and coronal shock wave are generated in the dynamic launching process of electromagnetic rail launcher. The shock wave is out of the muzzle from the front projectile to the tail of projectile,and the pressure distribution at the midpoint of projectile nose presentssymmetry. The resistance coefficient is related to the pressure distribution which presents a weak symmetry after the shock wave being out of the muzzle,which reachs a peak at the tail of projectile. When the projectile moves in the air,and the second peak pressure is greater than the first because of the superposition of the shock wave and its reflection. The farther the distance is,the smaller the reflection period is,the slower the pressure decays.