Abstract: The three-dimensional (3D) flow field around a rocket sled system in low subsonic testing velocities was simulated through 3D incompressible Navier-Stokes equations and the Realizable k-ε turbulence model. The wake flow characteristics of the rocket sled with and without the extension plate were obtained at different free stream velocities. Moreover, the difference of the wake flow fields were compared and analyzed between the rocket sled and the aircraft. Results show that the dynamic drag is about 4.8%~8.6% of the total weight of the rocket sled system corresponding to a drag coefficient about 0.65 for the free stream velocities in the range of 60 m/s to 90 m/s. The aerodynamic lift force, which is negative, is merely 0.84%~1.9% of the total weight, and the lift coefficient is just -0.005, suggesting that the effect of the aerodynamic lift can be omitted in the kinetic analysis of this rocket sled system. The dimensionless velocity difference in the detection location is less than 8%, and the dimensionless pressure difference is less than 0.5%. These differences indicate that the influence of the velocity on the wake flow field can be neglected. In addition, the wake flow fields are similar according to the comparison of the wake field between the rocket sled system and the aircraft. This similarity satisfies the requirement of the experimental test.