• The ceramic balls constrained by UHPC were used to replace ceramic plates in sandwich structure composite armor. • The influencing factors and damage mechanism of the ceramic balls/UHPC panel were analysed. • The 3D finite element simulation was used to analyse the process of penetration for more accurate simulation. • A mathematical probability model is established to select the diameter of ceramic ball. A composite armor with ceramic balls/UHPC panel was proposed by studying the penetration process of 10 mm armor-piercing projectile. The several factors, including the diameter of ceramic balls, the number of ceramic balls layers and the constraint effect, on the impact resistance of the targets were discussed. Results show that ceramic ball composite armor has excellent impact resistance. UHPC matrix can provide excellent constraint on ceramic balls, which is positive to their impact resistance. ANSYS/LS-DYNA was used to analyze the changes of velocity, damage and energy during the penetration process, after verifying the effectiveness of the simulation. Finally, the influence of different impact points on impact resistance was studied by simulation. The probabilistic impact model of ceramic balls composite armor was established. This model is used for selecting the best diameter of ceramic ball according to the projectile diameter. [ABSTRACT FROM AUTHOR]