Abstract: The investigation on the aerodynamic characteristics of a high speed ramjet propelled projectile with the design Mach number of 4 was performed by the method of numerical simulations. The internal and external drag acting on the projectile in passive flight phase was obtained through calculations. Variations of the drags were discussed at the range of Mach 4 to Mach 3. The results show that the inlet studied in current paper can restart at the design Mach number; the maximum total pressure recovery of the inlet is about 0.25 at the subcritical operational condition. When the passive flight Mach number decreases from 4 to 3, the internal drag coefficient changes scarcely, it is nearly 0.06. While the external drag coefficient increases from 0.16 at the Mach number of 4 to 0.21 at the Mach number of 3. The total drag coefficient ranges from 0.23 to 0.27 while the Mach number decreases from 4 to 3. The scale of friction drag is about 40% in internal drag and 20% in external drag.