The coupling of disk-corona structure is one of research hotspot in Active galactic nuclei (AGNs) and unclear so far. The studies of AGN disk reverberation indicate that the correlation and lag present between optical/ultraviolet(UV) and X-ray emission. Based on mentioned above, the corona is at a relative distance from accretion disk. In order to study the relative position of disk-corona conveniently, we consider the disk-corona as the lamp-post construction which assumes the corona as a point on the axis of the black hole spin. Accretion disk is located on the equatorial plane of black hole beneath the corona vertically. Strong gravity will be dominant near black hole. Therefore, the relativistic effect should be considered in disk-corona construction. (1) In the thesis, we study the interaction between disk and corona near black hole. We calculate the process of photons from corona to disk along with null geodesic by using the ray tracing method with lamp-post construction. Part of photons are absorbed by the accretion disk to heat the accretion disk and change the temperature structure. Then, accretion disk radiates the black-body spectra received by distant observer. Meanwhile, the distant observer will receive these photons emitted from corona directly as well. Therefore, the time lags will exist between photons of corona and disk. It's so called as the accretion disk reverberation. Another part of photons are reflected by disk to form the reflection spectra. Based on atomic physics, photons will be absorbed by matter of accretion disk and the spectrum has absorption features. If the reflection process is far away from black hole, the absorption features will be prominent. However, the absorption features will be smeared by strong gravity near black hole to generate the soft X-ray excess in 0.2-3 keV energy range. (2) In the thesis, we study the origin of the soft X-ray excess. Currently, there are some models to explain the soft X-ray excess origin. The main difference between these models is dependent on the disk-corona construction. Therefore, the study of soft X-ray excess will help us to understand the disk-corona construction in AGNs. We use the simultaneous X-ray observation data of XMM-Newton and Nustar on Sep. 24th, 2016 to perform the spectral analysis for ESO 362-G18. We adopt five models including the warm, optically thick corona and relativistically blurred high-density reflection models, or their combination to explore the origin of the soft X-ray excess. Through the spectral analysis, we find the double warm corona model can interpret the time-average spectrum and variability spectrum (RMS and covariance spectrum) well, however, this model will lead to a harder X-ray continuum radiated from corona. When the magnetic field dominants the physical process, it will accelerate the electrons by the first order Fermi acceleration produced by magnetic reconnection. If the double warm corona is true, the broad Fe K$\alpha$ line should not exist because the relativistic reflection component is excluded through the spectral analysis, which means that the narrow emission is sufficient to model the broad Fe K$\alpha$ line. The X-ray radiation region could be less than 50 times of schwarzschild radius. The second warm corona component is the main dominant mechanism in the low and middle temporal frequencies. The radiation of corona and distant reflection is dominant at high temporal frequency or a compacter scale. The distant reflection could be made of some moderate scale neutral clumps which correspond the high temporal frequency.
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