The authors study the electron collective excitations of the HgTe-CdTe superlattice with a simple model, taking into account the overlap of wavefunctions at the interfaces for interface states. The linear-response theory has been used to calculate the dielectric response of the superlattice to an external perturbation, including many-body effects, magnetic fields and electron-phonon coupling in a reasonable way for both intra- and inter-subband modes.