In this paper, the ballistic limit velocity of 12.7mm armor-piercing incendiary projectile impacting a typical lightweight ceramic composite armor made of boron carbide ceramic and multi-layered composite materials (carbon fiber/aramid fiber/ultra-high molecular weight polyethylene fiber) was obtained experimentally. The process of impact was numerically simulated by the FEM-SPH method, and the results pointed out the characteristics of the penetration and the energy dissipation rule of each component of the ceramic composite armor. On this basis, the influence of thickness changing of the carbon fiber core layer on the ballistic performance of ceramic composite armor was studied with a typical “sandwich” structure, and the results showed that: when the thickness ratio of ceramic tile to the backing panel is about 1.5, the thickness changing of the carbon fiber core layer has the greatest effect on the ballistic performance. Under this thickness ratio, when the ratio of ceramic tile thickness to bullet diameter is greater than 1, the increase of carbon fiber core layer thickness will cause the ballistic performance index (BPI) of the target to decrease while the ratio is less than 1, the BPI increases or holds at first, and then decreases.