The sabot discard process of shell piercing projectile has significance on the flight stability and strike efficiency of it. Aiming at the six degrees of freedom movement process of shell piercing projectile after leaving the chamber, a measurement method of sabot discard angle based on the principle of binocular vision was proposed. By setting some markers on the surface of projectile and sabot, the recognition and tracking of the markers were realized with the image processing and tracking algorithms. The spatial locations of these marker were calculated by combining with the binocular calibrated space parameters, and the discard angle of sabot relative to the projectile was obtained. Meanwhile, the accuracy of the method above was validated by experiment which was proved to be 2%. Taking the shell piercing projectile launching at initial velocities of 1550 m/s and 1750 m/s conducted in the laboratory as an example, the discard trajectories under different muzzle velocity were measured and analyzed. The results show that the faster the discard initial velocity is, the closer the discard trajectory is to the projectile.