The present work devotes to study the delocalization effect of 5f electrons for the actinide elements Th to Es using the quantum mechanical calculation based on the full symmetry group. Follow the definition of quantum mechanics for delocalization effect, it is founded that the variation of the delocalization energy and atomic volume for elements Th to Es is in the opposite tendency each other. The energy gap of HOMO- LUMO and atomic volume for elements Th to Es is nearly the 1 to 1 mapping, and they are the source and image one another.