The invention discloses a preparation method for formula (I) compounds, and the compounds are obtained by reacting a formula (II) compound with a formula (III) compound in a solvent in carbon monoxide atmosphere under catalysis of a heterogeneous-phase palladium catalyst. The reaction related in the method does not need strict waterless oxygen-free condition and does not need high pressure, is convenient and simple to operate, and possesses extremely good tolerance and universality on functional groups. Also the catalyst is extremely small in usage amount and is recoverable, reaction cost is low, and the preparation method is widely applicable to prepare alkyl/benzyl/aryl urea compounds. The formula (I) is R<1>-NH-CO-NR<3>-R<2>, the formula (II) is R<1>-N3, and the formula (III) is HNR<3>-R<2>, wherein R<1> and R<2> are same or different, and are mutually independently selected from aryl, heteroaryl, cycloalkyl, heterocyclic groups, alkyl, alkenyl, alkynyl, arylalkyl, heteroaryl alkyl, cycloalkyl alkyl, heterocyclic-group alkyl, aryl alkenyl, heteroaryl alkenyl, cycloalkyl alkenyl and heterocyclic-group alkenyl; and R<3> is selected from H or R<2>, or R<3> and R<2> are in connection for forming a ring.