To investigate the damage mechanism of TiB2P／2024Al composites in high-cyclic fatigue, axial fatigue experiments were carried out. SEM micrographs of fracture surfaces indicated that fatigue cracks mostly initiated at interior defects of the composites. The dominate damage modes were porous assembling type damage in matrix and interface debonding, scarcely any particle cracking. And coexistences of dimples and fatigue striations were observed in main propagation zone. The intrinsic mechanism governing the enhanced fatigue fracture characteristics are that, since the enforced particulate dimension is between sub-micron and micron level, lesser particles decrease stress concentration, disperse damage initiation sites, and increase the probability of crack deflection and bifurcation, then, the matrix plasticity exerts adequately. Therefore, the composites exhibit high fatigue resistance.