Abstract: The present invention relates to an engineered human factor VIII polypeptide, which includes at least two substituted amino acids in A1 domain of hFVIII. In some embodiments, the substituted amino acids comprise L50V and L152P. In some embodiments, the substituted amino acids further comprise one or more of amino acid substitutions selected from the group consisting of D20S, G22L, I61T, D115E, F129I, G132D, Q139E, and L159F. The present invention also relates to engineered hFVIII polypeptide encoding nucleic acid fragment, an expression vector or a rAAV vector contains such nucleic acid fragment, and a method of using engineered hFVIII polypeptide to treat hemophilia A patients.