The High-Energy Particle Detector (HEPD) is a range-calorimeter for the near-Earth measurement of electrons, protons and light nuclei fluxes up to few hundreds of MeV. HEPD will fly on board of the China Seismo-Electromagnetic Satellite (CSES), scheduled to be launched in July/August 2017. This mission will investigate possible correlations between geomagnetic properties (electromagnetic wave emissions, plasma properties and particle fluxes in the ionosphere and magnetosphere) and seismic events. The study of the solar-terrestrial environment, Coronal Mass Ejections (CMEs), Solar Energetic Particles (SEPS) events and low-energy cosmic rays are also within the scientific objectives of this mission. A detailed description of the HEPD and its characteristics will be reported.