The mechanisms of intermolecular hydroacylation of aldehyde are studied using DFT method in both neutral and cationic systems.The catalytic cycle involves three portions: C-H activation,the alkene insertion and C-C formation.The C-H activation step in neutral system but the reductive elimination step in the cationic system is the rate-determining step.Meanwhile,the alkyl group migration-phosphine ligand coordination is the favorable pathway compare with the phosphine ligand coordination-alkyl group migration pathway in the C-C formation stage.The electron-withdrawing groups decrease the energy barriers of the C-H activation in the benzaldehyde hydroacylation.The results will be helpful to design new catalyst with high catalytic activity in hydroacylation of aldehyde.