Jiaxin Han got his PhD from Shanghai Astronomical Observatory in 2013 and subsequently worked aspostdocs at the Institute for Computational Cosmology (Durham University, UK) and the Kavli Institute for the Physics and Mathematics of the Universe (IPMU, Tokyo University), before joining Shanghai Jiao Tong University in 2018 as a faculty member. His research is focused on astrophysical studies of the property and distribution of dark matter through various theoretical and observational approaches. He has been supported by the Marie-Curie foundation (EU), JSPS (Japan) and the national talent recruitment program.Dark matter halos are approximately virialized condensations of dark matter that serve as building blocks of the large scale structure and the birthplaces for galaxy formation. Although halos can be easily identified in numerical simulations, our understanding of many fundamental properties of halos still has a long way to go, especially in phasespace. In this talk, I will introduce our recent efforts in understanding halos from small to large scale, focusing on their dynamical state and boundary characterisation. I will show that incomplete phase-mixing of particles in halos leads to an intrinsic limiting accuracy for dynamical mass estimates, and provide possible solutions. I will also introduce a new characterisation of halo boundary that naturally describes the growing edge of a halo beyond the conventional virial radius, according to the clustering and velocity structure around halos.