In view of whether the reliability of the self-locking hoop of a certain type of armor-piercing projectile with retractable tail can meet the requirements of use in the process of launching and service handling, this paper puts forward the calculation and analysis of the reliability of the wing of the armor-piercing projectile with retractable tail. The expansion reliability and the folding reliability of the wings of a certain type of armor-piercing projectile with expansible fins are calculated, analyzed and verified by experiments. The calculation and the test results show that the self-locking hoop can be reliably unlocked after the muzzle during the firing process, and the self-locking hoop can be reliably retracted in the chamber and service handling.