The invention provides a method for preparing a lithium ionic sieve adsorbent. The method comprises the following steps: co-acting a raw material which is an aqueous solution of a lithium salt and a manganese salt by microwaves and ultrasonic waves to obtain a co-precipitation product, calcining the co-precipitation product to obtain a lithium ionic sieve precursor, and carrying out acid leachingon the lithium ionic sieve precursor to obtain the lithium ionic sieve adsorbent. The lithium salt and manganese salt mixed aqueous solution is used as the raw material, and precipitates under the co-action of the microwaves and the ultrasonic waves, the precipitate is calcined to obtain the lithium ionic sieve precursor with an ideal structure, a high purity and a high lithium content, and the lithium ionic sieve precursor is processed to obtain the lithium ionic sieve adsorbent. The lithium ionic sieve adsorbent has the advantages of stable structure and high adsorption capacity, and the method has the advantages of short time, low energy consumption and high controllability, and is of great significance to recycling lithium metal resources.