The dynamical behavior of entanglement ofr excitons in two quatum dots placed in two separately singlemode optical cavities driven by an external boradband two-mode squeezed vacuum is studied in the low exciton density regime. It is found that if the field in the two separated cavitied is initially prepared in a pure two-mode squeezed vacuum state, the excitons in the two quantum dots cna evolve into a pure entangled state only when the dissipation of the cavitied and excition modes is negligible. When the efect of the dissipation is included, the excitions will be in a two-mode Gaussian entangled mixed state whose properties are decided by the externally driven fiedld and the initial field. The dependence of the entanglement property of the excitons in the two quantum dots on the squeezing properties of the fields in the two cavities is also discussed.