Abstract: To study the effect of standoff on the penetration of the shaped charges in the air and water, this paper calculates the penetration into steel of WCu-pseudo-alloy shaped charges in the air and compares to those in the water using AUTODYN software. Numerical results show that there exists an optimum standoff for penetration both in the air and the water. The penetration in the water was even larger than that in the air when the standoff was less than four times charge diameter. Water acts as the standoff to some extent; in the meanwhile, it will shorten the jets by eroding the jet tip.