The present invention provides a method for preparing an siRNA for treating α1-antitrypsin deficiency. The siRNA is Fazirsiran. Fazirsiran is a double-stranded
RNA composed of a complementarily paired
sense strand and antisense strand. The preparation method comprises: mixing
sense strand substrates, antisense strand substrates, and an
RNA ligase, and using the
RNA ligase to catalyze the linkage between the
sense strand substrates and between the antisense strand substrates by means of phosphodiester bonds, to obtain a sense strand and an antisense strand, thereby obtaining Fazirsiran, wherein the sense strand substrates can form the sense strand, and the antisense strand substrates can form the antisense strand. Compared with the preparation of Fazirsiran by means of
chemical synthesis, the product obtained by the preparation method of the present application has higher purity and fewer impurities, and the
reaction conditions are mild, facilitating industrial large-scale production.