The HESS-2 experiment (High Energy Stereoscopic System) is an array of Cherenkov Telescopes measuring very high energies gamma-rays (beyond ~ 30GeV). This observatory is one of the most efficient ground-based instrument in the world: thanks to its large field of view, good angular resolution and high sensitivity it can detect and study the gamma emission of galactic sources at the highest energies. Celestial objects generating these high-energy gamma rays are the sites of cosmic rays acceleration, mainly electron / positron, whose fundamental mechanisms are subject of intense studies, both in observationally over the whole multi-wavelength spectrum as well as theoretically. In this context, the HESS collaboration conducted a survey of the galactic plane, which has allowed to realize a catalogue of nearly hundred gamma sources beyond 100GeV such as supernova remnants, pulsars wind nebulae, binary systems, ... and also a large number of unidentified objects and an unresolved or diffuse emission over several degrees around the supermassive black hole at the centre of the Milky Way. The purpose of this thesis focuses on the analysis of these data and new observations taken since, focusing on the most energetic gamma rays to look for the most powerful accelerators and to determine the nature of a large number of sources not yet identified. The data analysis methods will be optimized for the detection of very weak sources beyond a few TeV in order to identify isolated sources from diffuse emission, and finally to accurately characterize the energy spectrum of these components. The nature and distribution of isolated objects and the characteristics of the unresolved emission will then be studied in detail. A model of population synthesis, with their spatial distribution and their temporal evolution, could be developed from pre-existing tools. From these predictions, it will be possible to better understand the detected populations and the underlying particle acceleration mechanisms, to create a link between unresolved emission and populations of isolated sources. Understanding these populations of extreme accelerators and the link between the diffuse emission and the galactic astrophysical objects are a challenge since it is directly linked to the mystery of the origin of cosmic rays that spread throughout the Galaxy. It is also one of the key scientific projects of the observatory CTA (Cherenkov Telescope Array) made of more than hundred telescopes that will soon be built. The work of this thesis on the populations of very high energies sources observed by HESS-2 will be applied within the CTA consortium by preparing the development of the very first observation programs and of the tools to achieve the CTA catalogues.