Abstract: The present disclosure provides a method for extracting lithium using a resin adsorbent to pretreat low-grade deep brine, which relates to the technical field of lithium extraction from brine. In the present disclosure, resin adsorbent is used to perform adsorption pretreatment on the concentrated brine, which can adsorb organic impurities in the concentrated brine without adsorbing lithium ions, so that the concentration of lithium ions is almost unchanged compared with the feed material, with the subsequent manganese-based lithium adsorbent, the adsorption rate of lithium can be increased by 41%; At the same time, pretreating the concentrated brine using resin adsorbents has shorter steps, less materials, and does not produce a large amount of low-value product gypsum, which makes the lithium extraction process simpler and easier to operate, and reduces production costs.