The effect of support acidity on the cross-metathesis of ethylene and 2-butylene to propylene over heterogeneous Mo/HBeta catalyst was studied by density functional theory (DFT) calculations. The zeolite acidity was mimicked by changing the terminating Si-H bond lengths. Both of the initiating formation and propagating processes of Mo-carbene were investigated. It is found that there is a correlation between the zeolite acidity and the activation barrier. The influence of acidity on the initial Mo-carbene formation process is greater than that on the next process catalyzed by this active site. Theoretical calculations reveal that the heterogeneous catalyst with more acidic support could have better olefin metathesis activities, which is consistent with the experimental findings in the literature.