The invention relates to magnetic polyether for a water-based drilling fluid lubricant and a preparation method and application of the magnetic polyether. The magnetic polyether is obtained by graft copolymerization by taking hydroxylated magnetic nanoparticles as an initiator and epoxypropane and epoxybutane as structural units, wherein the hydroxylated magnetic nanoparticles are any one or moreof hydroxylated Fe3O4, Ni-Fe and cobalt oxide nanoparticles, and the magnetic polyether contains the following components in percentage by weight: 5%-20% of the magnetic nanoparticles, 20%-60% of epoxypropane chain segments and 10%-20% of epoxybutane chain segments. The magnetic polyether for the water-based drilling fluid lubricant provided by the invention shows an excellent targeting lubrication effect, significantly improves the adsorption effect of the lubricant on the surface of a drilling tool, also has the advantages of long lubrication duration, good recycling stability and good compatibility with different water-based drilling fluids, and is especially suitable for long open hole section horizontal wells.