Molecular dynamics simulation was performed to obtain the formation energy of vacancy clusters in silicon crystal and learn relevant factors,in which the influence laws and their mechanisms of model system size,configuration of vacancy cluster and vacancy number on the formation energy of vacancy cluster were revealed.The results show that the size of model system and configuration of vacancy cluster have little effect on the formation energy of vacancy cluster in general;the size of 3×3×3 model system is more suitable for the calculation and analysis of the formation energy;the minimum formation energy increases linearly as vacancy number increasing is less than 6;the formation energy of vacancy cluster in essence depends on the number of broken Si-Si bonds as well and energy.