The invention relates to a multifunctional anti-crack additive and a preparation method of the multifunctional anti-crack additive. The multifunctional anti-crack additive comprises the following components: 25%-40% of calcium oxide expanding clinker, 1%-3% of dextrin and the balance of coal ash. The preparation method comprises the following steps of: grinding the calcium oxide expanding clinker and the coal ash to have the specific surface area of 200-400m<2>/ kg in proportion; and evenly mixing the ground materials with the dextrin weighed in proportion to obtain the multifunctional anti-crack additive provided by the invention. The multifunctional anti-crack additive provided by the invention can reduce the temperature rise, and can promote the effective expansion of calcium oxide expansion components, so that the dual-adjustment of the concrete structure temperature field and the calcium oxide components expansion course can be realized.