The invention relates to a preparation method of a compound represented by a formula (I). The compound is prepared by reacting a compound represented by a formula (II) with a compound represented by a formula (III) in a solvent under the catalysis of a palladium catalyst in carbon monoxide atmosphere, wherein X is O or N; N is 0 or 1; when X is O, n is equal to 0; when X is N, n is equal to 1; R1 is selected from aryl, heteroaryl, alkyl, alkenyl or alkynyl; R2 is selected from aryl, heteroaryl, alkyl, alkenyl or alkynyl; R3 is selected from H, R2 forms a ring, or R2 and R2 are linked to form a ring; R4 is N3 or a halogen atom; when R4 is the halogen atom, a system further contains sodium azide. The preparation method has the beneficial effects that the reaction does not require strict anhydrous and anaerobic conditions and high-pressure carbon monoxide atmosphere, the operation is convenient and simple, and the reaction has very good tolerance and universality to functional groups; meanwhile, the use level of a catalyst is extremely low, the reaction cost is very low, and the method can be widely applied to the preparation of sulfonylurea compounds.