The invention relates to the field of gene engineering and cytobiology, in particular to a preparation method for efficiently amplifying NK cells by utilizing trophoblasts. The construction method comprises the following steps: (1) constructing a pHR-mbIL-21 plasmid vector, a pHR-4-1BBL plasmid vector and a pHR-MICA plasmid vector; (2) preparing recombinant lentiviruses by using pHR-mbIL-21, pHR-4-1BBL and pHR-MICA plasmid vectors respectively; (3) preparing K562-mbIL-21-4-1BBL-MICA trophoblasts; (4) extracting PBMC cells; and (5) carrying out in-vitro amplification on NK cells. The inventionprovides the preparation method of NK cells. The method employs the step of independently constructing plasmid vectors for expressing mbIL-21, 4-1BBL and MICA molecules, K562 is infected with recombinant lentivirus, the NK cells can be prepared, the preparation method overcomes the defects in the prior art, the K562 cells simultaneously expressed by IL-21, 4-1BBL and MICA molecules are used as trophoblasts for amplification culture of the NK cells, the amplification multiple of the NK cells reaches up to 890 times, the purity of the prepared NK cells reaches 92.2%, and the repeatability of theamplification multiple between different PBMC cells is good.