Prof. Ruoyu Liu obtained his doctoral degree from the University of Heidelberg in 2015. Before he joins Nanjing University, he worked as a postdoctoral researcher in Max-Planck-Institute for Nuclear Physics (MPIK) and Deutsches Electron-Synchrotron researcher center (DESY) respectively for two years. His research interest mainly focuses on (but not limited to) the astroparticle physics and the high-energy astrophysics, including the origin of high-energy cosmic rays and high-energy neutrinos, the radiation processes in dynamic astrophysical objects such blazars, gamma-ray bursts, pulsar wind nebulae, etc, as well as their roles as the accelerators of cosmic rays.The gamma-ray halo of pulsar is a new species of Galactic gamma-ray sources discovered three years ago by the High Altitude Water Cherenkov observatory (HAWC). It generally extends a few tens of parsecs around the pulsar and is believed to arise from the inverse Compton scattering of cosmic ray electron/positron pairs that escape from the pulsar wind nebula into the ambient interstellar medium. The pulsar halos may have important contribution to the Galactic diffuse TeV gamma-ray emission. Besides, the spectral and morphological features of the pulsar halos can shed light on the transport mechanism of cosmic rays in the Galaxy and the local interstellar magnetic field. I will overview the studies on the pulsar halo up to date with a slightly additional focus on the results of our group.