Based on the assumption that a solid or a liquid which consists of a vast number of atoms can be regarded as a collection of atom clusters which themselves can be regarded as particles. a renormallzation procedure has been applied to the cluster system in oder to produce a new reduced system having the same scale as the atomic one. This new system consists of particles of atomic size but having the same mass as the original clusters. Then it is shown that molecular dynamics simulation carried out on this system using the same interatomic potential as that of the original atcmlc system reproduces results corresponding to those of the original huge atomic system with regard to phenomena of a scale larger than that of clusters. We then discuss the damping effect which should be introduced in the cluster system. An example of a numerical algorithm for the variable scale molecular dynamics developed based on the above discussion is also presented.