In order to optimize the similarity test for target plate penetration resistance, using the revised Tate simplified penetration model, which was proposed based on the hydrodynamic analogy, the general form of similarity law when projectile penetrating target considered the strain rate effect of the projectile and target panel at the same time was derived on the basis of similarity theory. A series of calculations and analyses were carried out by engineering calculation method. The results showed that the geometrical similarity law of penetration problem was inaccurate when considering the effect of the projectile and target plate strain rate at the same time, and this phenomenon became more obvious with the increase of scale ratio. The modified formula for geometrical similarity law was given by fitting the calculation results.