The alpha disk model is widely used to describe the accretion disk structures around supermassive black holes, even though it cannot explain many observed properties of AGNs. I will describe our series of global 3D radiation MHD simulations of AGN accretion disks and discuss how these simulations can improve our understanding of accretion systems for both single and binary black hole cases. These simulations cover a wide radial range with a variety of accretion rates. Near the inner region around the black hole, I will discuss how the interplay between turbulence due to magneto-rotation instability and radiation transport determines the properties of corona in AGNs. For the outer part of the disk, I will describe a thermally stable disk structure that can explain many properties of the UV/Optical emission from AGNs. Finally, I will also show how the strong radiation pressure can affect the angular momentum balance in binary black hole systems.