A systemical computational study was performed to explore the mechanism and origin of selectivities on the organocatalytic arylation of azonaphthalenes with α-chloroaldehydes. The calculated results reveal that the nucleophilicity of active sites and the hydrogen bonds respectively regulate chemo- and stereoselectivities and, for the first time, N-heterocyclic carbene (NHC) can act as a multiple functional base (MFB) catalyst in one system.