| In this thesis, we present the studies of the high energetic gamma-ray radiative mechanism, central black hole mass, the Doppler factor, and jet's composition of active galactic nuclei, etc..High energy gamma-rays are important probes of the Universe. Unlike radiation at longer wavelengths, gamma-rays are not attenuated significantly within the Galaxy. As such, they provide an unobstructed view through the plane of the Galaxy except for regions which contain high densities of low energy photons (or virtual photons in regions of high magnetic fields) where Very High Energy (VHE) gamma-rays are attenuated via photon-photon pair production. With new experiments, such, as GLAST and VERITAS on the horizon, we are entering an exciting period for gamma-ray astronomy. The gamma-ray waveband has provided a new spectral window on the universe and has already resulted in dramatic progress in our understanding of high energy astrophysical phenomena.Within the unification model, the underlying scenario for all AGNs is intrinsically similar. At the very center of the galaxy there is a supermassive black hole (106 to 1010M?) which accretes galactic matter forming an accretion disk. Broad emission lines are produced in clouds orbiting above the disc at high velocity (the Broad Line Region, BLR), and this central region is surrounded by an extended, dusty, molecular torus. Narrower emission lines are produced in clouds moving much farther from the central black hole. Unification of different AGN classes is achieved taken into account the intrinsic anisotropy of the phenomenon. It is generally accepted that blazar gamma-ray emission originates in relativistic jets. Blazar general observed features show: a) strong flux variability, b) strong spectral variability, especially when flaring, and c) the dominance of the gamma-ray emission over all other wavelengths.There are two kinds of models on γ-ray radiative mechanism of AGN: leptonic models and hadronic models. Both scenarios have to explain the...
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