The invention discloses a preparation method of a highly dispersed TiB2/A356 composite material, and belongs to the technical field of material preparation. The highly dispersed TiB2/A356 composite material is prepared from the components in percentage by mass: 3.0-10.0% of reinforced particles of TiB2 and 6.5-7.5% of a matrix alloy Si, 0.35-0.45% of a matrix alloy Mg and the balance of Al; and the reinforced particles of the composite material are TiB2 particles with a size of less than 1 [mu]m, and the matrix image composition mainly includes alpha-Al, Mg2Si and eutectic Si. An Al-TiB2 intermediate alloy is prepared by a melt self-propagation direct synthesis method, and Al powder, Ti powder, TiO2 and H3BO3 are used as raw materials to prepare the TiB2 particles with a stable mass fraction and a small average size. The preparation method adopts a two-step method to prepare the composite material, the Al-TiB2 intermediate alloy is firstly prepared, the condition that loss to the alloycomposition is caused due to the fact that a in-situ reaction is directly performed in the Al-Si-Mg matrix alloy is avoided, the Al-TiB2 intermediate alloy is used as a substrate, an aluminum ingot is added to adjust the composition, and the composite material is prepared.