In the past decades, studies of the Milky Way have entered a golden era of large-scale surveys. The Gaia satellite provides precise positions, proper motions, and parallaxes for billions of stars, while ground-based spectroscopic surveys, such as LAMOST, deliver radial velocities and metallicities for nearly ten million stars. In addition, medium- and narrow-band photometric surveys, as well as Gaia’s slitless spectroscopic surveys, provide atmospheric parameters for hundreds of millions of stars. This talk will first summarize our efforts in measuring stellar parameters from these surveys, and then present our work on understanding the assembly history of the Milky Way—particularly its early phase, when the proto-Galaxy formed—and its dark matter distribution, based on the measured parameters of a very large number of stars.