The highly excited atoms have a strong Van der Waals interaction as compared with the ground-state atoms, which can block the excitation of neighboring atoms and forming the blockade effect. In this work, the interaction between highly excited atoms is calculated using the perturbation theory, the interaction of nS and nD pair states and the dispersion coefficients are obtained. This shows that the interactions of the SS for both Rb and Cs atoms are repulsive, whereas the interaction of DD states is repulsive for Cs and attractive for Rb.