Large-scale conformational change is frequently essential for the proper functioning of macromolecules,especially for membrane transporters and channels,which open and close in response to external signals.Unfortunately,the time scale of such slow conformational changes typically exceeds the technical limit of conventional molecular dynamics (MD) simulations,which can only observe sub-millisecond molecular events in general,due to the limitations on time step and computer hardware.In this work,we will present our recent progresses on simulating the large-scale conformational changes of several membrane transporters and channels.By combining the enhanced sampling techniques and rigorous free energy calculations,we not only observed the large-scale conformational changes of a few membrane proteins (including primary and secondary active transporters,facilitators,as well as voltage-gate ion channels),but also identified the reaction pathways and evaluated the free energy changes along the paths for these proteins.Eventually,molecular mechanisms could be inferred from these quantitative evaluations.