A method for preparing a lithium extraction adsorbent and an application of the lithium extraction adsorbent are provided. The method includes: (i) forming a homogeneous casting liquid by stirring a metal-based lithium ion sieve, an organic carrier, and a functional material; (ii) adding the homogeneous casting liquid dropwise to a solidifying liquid to obtain gel particles, wherein the solidifying liquid consists of sodium hydroxide and ethanol; and (iii) washing the gel particles to neutrality with deionized water to obtain washed gel particles, followed by placing the washed gel particles in a glutaraldehyde solution for stirring to crosslink for 0.5 h to 12 h to obtain crosslinked gel particles, freeze-drying the crosslinked gel particles to obtain the lithium extraction adsorbent, wherein a usage condition of the lithium extraction adsorbent includes: before use, activating the lithium extraction adsorbent by placing the lithium extraction adsorbent into an alkali activator for stirring for 0.5 h to 12 h, and washing the lithium extraction adsorbent to neutrality with deionized water.