A preparation method for imidazoisoindole derivatives. Specifically provided is a preparation method for imidazoisoindole derivatives represented by a formula (I). The method comprises : dissolving a compound represented by a formula (II) to obtain a compound represented by a formula (III) with high optical purity; and using the compound represented by the formula (III) as a raw material to implement chemical reactions. The obtained final product has high optical purity and low cost, is more economical, and is more suitable for industrial production.