The medium caliber armor piercing projectiles, commonly being used against armored and aerial targets, have high kinetic energy and in practice, it is impossible to prevent these projectiles from penetration through different types of targets. So this is essential to demonstrate a solution to repel these projectiles by studying on behavior of the targets. In this study, numerical simulation of oblique penetration of medium caliber armor piercing projectile through the flat targets of GLARE3 2/1 and GLARE5 2/1 has been investigated by ABAQUS finite element software, and using explicit-dynamic solver. 625m/s and 1250m/s strike velocities and 0, 30, 45, and 60 degree strike angles have been studied. Damaged area have been investigated. To verify the solving method, an experimental equation, which has determined the penetration energy of a thin GLARE target, has been used. Results have shown that some special phenomena (e.g. asymmetric petalling, and small-cracks formation) appear when penetration occurs obliquely. This is also has been shown that lower strike velocity, and higher strike angle will result in higher target damage. Furthermore, delamination of target has been investigated.