GRAVITY is a new instrument to coherently combine the light of the European Southern Observatory Very Large Telescope Interferometer to form a telescope with an equivalent 130-meter diameter angular resolution and a collecting area of 200 square meter. With a phase-tracking on stars as faint as K~10 mag, phase referenced interferometry is able to observe objects fainter than K~15 mag with minute-long coherent integrations. Since the commissioning in 2015, GRAVITY has produced a series of high impact scientific results, including observations on Galactic center, exoplanet atmosphere, microlensing event, and active galactic nuclei broad emission line region. In this talk, I will provide an overview of GRAVITY and its scientific highlights. I will mainly focus on the results and progresses on our active galactic nuclei large project, including the studies of the broad emission line regionkinematics, hot dust emission in near-infrared, as well as the plan of GRAVITY upgrade that enables the all sky extragalactic science in the near future.