Density functional theory (DFT) calculations were performed to study the detailed reaction mechanism of the cross-metathesis of ethylene and 2-butylene over heterogeneous Mo/HBeta catalysts. The whole process is divided into two stages: the initiation of Mo-carbene species from Mo-oxo precursors and the propagating process by these active sites to yield propylene. The formation of initial Mo-carbene takes place via the endothermic addition and the subsequent decomposition of the oxametallacyclobutane intermediate. In the propagating stage to yield the final products, Mo=CHCH3 firstly reacts with ethylene to form Mo=CH2, which would further react with 2-butylene to give another propylene molecule. The oxidation states of the Mo species have great influences on the reactivities associated with these two stages. It is unfavorable for Mo-IV-oxo precursors to produce Mo-alkylidene species compared with Mo-VI and Mo-V sites. The energy barriers indicate that the Mo-VI and Mo-V-alkylidene species could catalyze the olefin metathesis reaction, but Mo-V ones are more preferred to be the active sites. The calculation results are consistent with our previous XPS results. (C) 2010 Elsevier B.V. All rights reserved.