The invention discloses a method for preparation of viscose fiber using sweet sorghum stalk. The cellulose pulp of sweet sorghum stalk is made by using sweet sorghum stalk as raw material. The viscose fiber is produced by cellulose pulp of sweet sorghum stalk. The steps of preparing viscose fiber using sweet sorghum stalk are as follow: stock, cooking, discharge, dressing by washing, desanding, chlorination, basification, bleeching by sodium hypochlorite, washing, condensing, paper making, dipping, compression, aging, etiolation, grinding, dissolution, blending, filtrating, debubbling, filtrating, spinning, drafting, post-processing and etc. The invention can effectively removed the impurities in the sweet sorghum stalk, therefore a high-quality viscose fiber of sweet sorghum stalk is obtained, with high cellulose content, good whiteness, lower impurity contents of pentose, crozzle and so on.