Hot accretion flow is widely believed to be essential for our understanding of low-luminosity AGNs (LLAGNs) and black hole X-ray binaries (BHBs) in their hard (and quiescent) state. In this talk, I will first review the current status of accretion theory. The progresses viewed from fundamental physics perspective are angular momentum transport, turbulent heating mechanism, and outflow/wind; from accretion mode perspective include magnetic-arrested disk (MAD) and high-\dot{M} hot accretion flow. Applications of these progresses in LLAGNs and BHBs will also be addressed. More specificly, I will use both the index-lumonosity correlation and the radio-X-ray correlation as tools to probe the change in accretion mode. I will also discuss the radiative properties (efficiency and SED) of MAD.