In order to set rationalized armor-plates and effectively estimate armor’s ballistic performance, research on the theory of energy balance by pictures, and this method is used for estimating armor-plates’ ballistic performance. Results are validated by ballistic experiments of steel and basalt fiber composites which reinforced by unsaturated polyester. Studies show that: this method leave out of account armor’s damage mechanism, and simplify parameters, but get high precision of estimate. The V50 or Vt which is estimated by energy balance has a lower than 50m/s deviation, and relative deviation lower than 10%. It can meet engineering demands.