The invention discloses an emodin di-n-octyl quaternary ammonium salt with anti-leukemia activity and a preparation method thereof. The emodin di-n-octyl quaternary ammonium salt is methyl di-n-octyl-[2-(4,5-dihydroxyl-7-methoxyl-9,10-anthraquinonyl) methyl] ammonium salt. Experiments prove that an emodin derivative, i.e. the emodin di-n-octyl quaternary ammonium salt has proliferation inhibition effects of different degrees on four leukemia cell lines K562, NB4, U937 and Jurkat and can be used for preparing a medicament for treating leukemia. The emodin derivative methyl di-n-octyl-[2-(4,5-dihydroxyl-7-methoxyl-9,10-anthraquinonyl) methyl] ammonium bromide has the advantages of simple preparation process, mild preparation conditions and high yield of reaching up to over 50 percent; and in-vitro cancer cell inhibition experiments show that the four leukemia cell lines K562, NB4, U937 and Jurkat can be effectively killed off.