Abstract: The present invention provides a siRNA for inhibiting HTT gene expression and a precursor thereof, an expression vector comprising the siRNA or the precursor thereof, application thereof in preparation of a drug for treating Huntington's disease, and a pharmaceutical formulation and pharmaceutical composition containing the siRNA, the precursor or the expression vector. The siRNA is selected from the following: SEQ ID NO:1, SEQ ID NO:2. SEQ ID NO:3, SEQ ID NO:4, SEQ ID NO:5, or a combination thereof.