| In this thesis, the basic properties, classification, uniform model of the active galactic nuclei (AGNs) have been reviewed. Then, we also discussed the variability and the radiation mechanism of blazars, and detailed present our research work during PhD.Blazars are the brightest and most variable high-energy sources among ac-tive galactic nuclei, and their nonthermal continuum emission from redio band extend up to X-ray and7-ray frequency, and they exhibit rapidly, large ampli-tude, and correlativity variability. Variability is one of the important obser-vational characteristics of blazars, and the periodicity of outbursts in blazars is particularly interesting, because variability analysis is one of the powerful methods in understanding their central engines and energy production pro-cesses. Therefore, we analyze the variability of two objects and research their central structure. We compiled and analyzed the variability data of 3C 279 at 22 GHz,37GHz, optical R band and X-ray band, and found it is an extremely active object with quasi-periodic outbreaks. A period of P= 130.6±1.3 days was consistently confirmed by three methods:the power-spectrum method, the discrete correlation function (DCF) method, and the Jurkevich method. Based on the relationship between observed period Pobs and the precession period Pp given by Rieger and our result, the precession period of jet in 3C 279 is Pp (?)29.6 yr, which is completely consistent with the precession period of jet of about 30 yr obtained by Carrara et al.. This suggests that there is a precession jet in 3C 279 and the variability period of about 130.6 days that we obtained is most likely caused by the helical motion of the jet.In addition to the variability analysis of 3C 279, we also researched the variability characteristics of Seyfert galaxiesⅢZw 2 which is the other sub-class of AGNs. We have presented the radio light curves of the Seyfert galaxiesⅢZw 2 at 22 and 37 GHz taken from the database of Metsahovi Radio Ob-servatory, and the light curves show great activity with very complicated non-sinusoidal variations. Period of Pobs= 5.14±0.19 yr was consistently identified by three methods:the Jurkevich method, the power spectrum intensity estima-tion method and the discrete correlation function method, which is consistent with the qualitative result obtained by Brunthaler et al. (2003). The variability period of about 5.14 yr inⅢZw 2 is caused most likely by the helical motion of the jet.Blazars are a typical subclass of AGNs and their spectral energy distribu-tions reflect the muliband radio property. The similar and different SEDs of different subclasses of blazars indicate that there are similar or different physies mechanism and limit condition. Searching the connection of different types of blazars would substantially promote our understanding about the fundamental nature of blazars. Therefore, the relationship among different types of blazars is very interesting. We compiled the optical, X-ray andγ-ray data for 54 Fermi blazars and studied the relationship between the broad band spectral index aox andαxγ, as well as the relationship between the intrinsic composite spectral indices axox andαγxγfor this sample. The relationship between axox andαγxγreveals that FSRQs and LBLs follow a continuous trend, which is consistent with previous results, whereas HBLs follow a separate distinct trend. Even so, a unified scheme is also revealed fromαxox-αγxγdiagram when all three subclasses of blazars are considered.
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