In order to study the deceleration effect of explosive reactive armor(ERA) on long rod type tungsten steel armor piercing projectile, the long rod armor piercing projectile model was designed by using LS-DYNA finite element software, and the numerical model of long rod armor piercing projectile penetrating explosive reaction armor with different speeds and angles of attack was established and the penetration process and speed of each part of the armor-piercing projectile were analyzed.The results show that the explosive reactive armor has obvious deceleration effect on the long rod penetrator, which is related to the attack angle between the axis of the penetrator and the normal of the reaction armor.The larger the angle of attack is, the better the deceleration effect is, and the stronger the protection performance of the explosive reaction armor is; the deceleration effect of the projectile body in the process of penetration has hysteresis, and the farther away from the warhead, the slower the starting time of deceleration.A new type of explosive reaction armor piercing projectile with two-stage warhead is designed, which can provide useful reference for the designers of anti-Armor Weapon System in the aspect of structure optimization.