Using the traditional zone-block apparatus for the projectile velocity test, the air resistance is always ignored and the projectile is assumed to be moving in a straight line at a uniform speed. Based on the principles of aerodynamics and theoretical mechanics, a method for measuring the instantaneous velocity of projectiles using two sets of zone-block velocity measuring apparatus was proposed. The velocity attenuation coefficient Bof the projectile flying in the test area was calculated by using the velocity values of two velocity measuring points separated from a certain distance. Then the instantaneous velocity of any point in the trajectory near the test area could be calculated from the Bvalue. Simulation analyses show that the relative measurement error of this method within 0.8 times the speed of sound is less than 0.01%, which is much lower than the engineering error requirement of 0.1%. The slingshot, air gun and rifle live ammunition experiments find that the measurement accuracy of the projectile flight speed within 0.8 times or more than 1.2 times the speed of sound is not lower than the 0.1% accuracy of the zone-block apparatus, which verifies the feasibility of this method. The research provides new ideas and methods for the design and optimization of the ballistic comprehensive parameter measurement system.